![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Cell Signaling Unit, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Parc de Recerca Biomèdica de Barcelona, E-08003 Barcelona, Spain,1 Swiss Federal Institute of Technology Zurich (ETH), Institute of Biochemistry, Zurich, Switzerland2
Received 16 January 2007/ Returned for modification 14 March 2007/ Accepted 23 March 2007
 |
ABSTRACT |
|---|
 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
It has been reported that SAPKs can modify gene regulation by direct phosphorylation of transcription factors, both activators and repressors, and can modulate factors involved in chromatin remodeling and structure (5, 16). In yeast, Hog1 participates initially to make cells competent for gene expression (23), and in addition, it is intimately recruited to chromatin in response to osmostress (2). Once bound to chromatin, apart from its role in elongation (20), Hog1 is able to regulate transcription initiation by several mechanisms: direct phosphorylation of several transcription factors (i.e., Sko1 and Smp1) (6, 21, 21), recruitment of the Rpd3 histone deacetylase complex, which promotes the modification of the chromatin at the promoters (7), and stimulation of the recruitment of RNA polymerase II (Pol II) (1). Thus, the specific chromatin association of Hog1 with stress-responsive promoters has shown an important function for this kinase in the regulation of transcription initiation.
In eukaryotic cells, transcription initiation by RNA polymerase II is a highly regulated process that requires the coordinated activities of a large number of factors. An important and conserved class of factors consists of coactivators, multiprotein complexes that are recruited to cognate promoters, such as SAGA (Spt-Ada-Gcn5), TFIID, and Mediator. These coactivators lead to Pol II recruitment and subsequent preinitiation complex (PIC) formation to facilitate transcription initiation (14). SAGA is a multisubunit cofactor for Pol II transcription that regulates chromatin, and it is required to deliver TATA-binding protein to promoters (27). The molecular architecture of SAGA has depicted different subcomplexes with distinct regulatory functions (31). It has been reported that SAGA and TFIID make overlapping contributions to the expression of Pol II-transcribed genes (17). However, TFIID function seems to predominate in the transcription of 
90% of the yeast genome, whereas SAGA might have an important role in the transcription of 10% of the genes, largely stress-induced and highly regulated genes (13). Strikingly, genes that are commonly up-regulated during general environmental stress are strongly biased toward being SAGA dominated. This suggests that SAGA might be particularly important for genes that respond to stress. There are several aspects of SAGA that are still uncertain, such as what determines SAGA specificity for certain genes and its relationship in time and space with other components of the PIC (e.g., SWI/SNF, Mediator, TFIID, etc.). For instance, in the GAL1 promoter, SAGA recruitment by Gal4 precedes that of Mediator (4), whereas at the HO gene, there is simultaneous recruitment of SWI/SNF and Mediator which precedes SAGA recruitment (9). Actually, recent results suggest that Mediator is not a stoichiometric component of the basic Pol II machinery but rather a complex selectively required by specific activators. Furthermore, it is also found in some inactive promoters prior to transcription to mark regulatory regions ahead of input stimulatory signals (3, 8). Thus, it seems that the ordered assembly of the PIC varies depending on specific promoters and activators.
In response to osmostress, the ATF/CREB-related transcription factor Sko1 regulates several genes under the control of the Hog1 mitogen-activated protein kinase (MAPK) (19, 29, 21). Interestingly, Hog1 phosphorylation switches Sko1 activity from a repressing to an activating state, which involves the recruitment of the SWI/SNF and SAGA complexes (22). However, the relevance of SAGA in osmostress transcription and how it is targeted to the osmostress promoters remain unclear.
In this work, by an exhaustive genetic approach, we have defined the roles of the SAGA and Mediator complexes in osmoadaptation. SAGA and Mediator are targeted by Hog1 at the osmoresponsive genes, where they play a critical role in osmostress gene expression. Interestingly, whereas Mediator is essential for proper gene induction under any osmostress condition, the role of SAGA at the promoters seems to be stress dependent, which results in a differential promoter regulation in response to the strength of the stimuli perceived by the cell.
|
MATERIALS AND METHODS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
1 leu2-0 met15-0 ura3-0) and derivatives containing chromosomally integrated ADA2-TAP, ADA1-TAP, SPT20-TAP, SPT3-TAP, MED2-TAP and SPT8-TAP, YEN233 (MATa SPT20-MYC9-KAN), YMZ45 (MATa SRB4-HA6-HIS3), YMZ53 (MATa hog1::kanMX4 SRB4-HA6-HIS3), YMZ33 (MATa HOG1-HA6-HIS3), YMZ34 (MATa spt20::kanMX4 HOG1-HA6-HIS3), YEN225 (MATa pgd1::kanMX4 HOG1-HA6-HIS3), YEN239 (MATa SPT20-HA6-HIS3), YEN240 (MATa pgd1::kanMX4 SPT20-HA6-HIS3), YMZ46 (MATa spt20::kanMX4 SRB41-HA6-HIS3), YMZ48 (MATa HOG1-MYC18-KAN SRB4-HA6-HIS3), YEN252 (MATa spt20::kanMX4 SRB4-MYC13-TRP) YMZ65 (MATa sin4::kanMX4 SPT20-HA6-HIS), YMZ66 (MATa TBP1-MYC18-HIS), YMZ68 (MATa spt20::kanMX4 TBP1-MYC18-HIS), YMZ69 (MATa spt20::KanMX4 MED2-TAP). The strain YEN234 (MATa ura3 leu2 trp1 his3 hog1::TRP1 spt20-MYC9-KAN) is derived from wild-type S288C. Strain SGY190 (SRB4-MYC13-TRP) and the taf1ts, taf2ts, and srb4ts strains and their respective wild-type strains were kindly provided by M. R. Green (University of Massachusetts). (ii) Plasmids. The pRS426TEG1, pRS426TEG1-Hog1, pRS426TEG-Srb4 plasmids, expressing glutathione S-transferase (GST), GST-Hog1, and GST-Srb4, were described previously (1).
High-throughput osmotic screen. An ordered array of 4,644 MATa viable haploid yeast gene deletion mutants (Saccharomyces Gene Deletion Project, obtained from EUROSCARF) in duplicate was replica pinned onto yeast extract-peptone-dextrose (YPD) and YPD plus 2.2 M sorbitol. The screen was performed by using an automated system. For automated arraying, yeast cells were transferred using the Biomek FX robot and a 384-floating-pin replicator (Biomek FX HDR 384-pin plate) as described previously (28). The screen was performed two times, and plates were incubated at 30°C for 3 days before scoring.
Chromatin immunoprecipitation. Chromatin immunoprecipitation was performed as described previously (2, 15). Yeast cultures were grown to early log phase (optical density at 600 nm [OD600] = 0.6 to 1.0) before aliquots of the culture were exposed to osmotic-stress treatment (0.4 M or 1.2 M NaCl) for various lengths of time. For cross-linking, yeast cells were treated with 1% formaldehyde for 20 min at room temperature. Primer mixes were adjusted for balanced signals. We used oligonucleotides to amplify regions of STL1 ([–181/+117]/[–372/–112] and +1000/+1280) to analyze binding of the Pol II, Hog1, SAGA, and Mediator proteins to the promoter or coding region, respectively. As internal controls, TEL1 (chromosome VI; coordinates 269606 to 269783) and GAL1 (–273/+132) were used. Immunoprecipitation efficiencies were calculated in triplicate by dividing the amount of PCR product in the immunoprecipitated sample by the amount of control. Data are presented as n-fold immunoprecipitation relative to results for the TEL1 or GAL1 control.
GST pull-down experiments. To analyze the association of Hog1 with components of the SAGA complex, two milligrams of yeast extract, from cells expressing GST or GST-Hog1 and specific TAP-tagged proteins, in buffer A (50 mM Tris-HCl [pH 7.5], 15 mM EDTA, 15 mM EGTA, 0.1% Triton X-100, 150 mM NaCl, 2 mM dithiothreitol plus antiproteases and phosphatase inhibitors) was incubated with 50 µl of glutathione Sepharose 4B beads overnight at 4°C. To analyze the association of SAGA with Mediator, two milligrams of yeast extract from cells expressing GST or GST-Srb4 and Spt20-Myc was treated as above. The beads were washed extensively with buffer A, resuspended in loading buffer, and resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The antibody used to detect the TAP-tagged proteins was the PAP antibody from Sigma. Similarly, coimmunoprecipitation of Hog1 with Mediator proteins was performed with two milligrams of yeast extract from cells expressing GST or GST-Hog1 and Srb4-Myc and treated as above. The presence of Mediator in the coimmunoprecipitates was detected with the monoclonal Myc antibody.
Gel filtration analysis. One liter of culture of logarithmically growing cells expressing tagged Srb4-Myc or Med2-TAP was subjected to osmostress (1.2 M NaCl, 100 min) and harvested by centrifugation, and cells were lysed in the presence of buffer A. Crude extracts were cleared, and the supernatant was passed through a 0.45-µm filter. Five milligrams of protein was loaded onto a Superose 6 HR 10/30 column (Amersham Pharmacia Biotech). The flow rate was adjusted to 0.3 ml/min, and 0.5-ml fractions were collected. Elution profiles of tagged proteins were analyzed by Western analysis and compared to the elution profile of known standards.
Northern blot analysis. Yeast strains were grown to mid-log phase in rich medium and then subjected to osmotic shock (0.4 M NaCl, 1.2 M NaCl, or 1.8 M sorbitol) for various lengths of time. Total RNA and expression of specific genes were analyzed using labeled PCR fragments containing the entire open reading frame (ORF) of STL1 (1.7 kbp), CTT1 (1.7 kbp), GRE2 (1.0 kbp), RPL28 (0.45 kbp), HSP12 (0.3 kbp), or TRX1 (0.3 kbp) or the noncoding exon of RDN18-1 (1.8 kbp). Signals were quantified using a Fujifilm BAS-5000 phosphorimager.
|
RESULTS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Thus, we performed a high-throughput screen by robotically pinning an ordered array of 
4,700 haploid yeast deletion mutants onto YPD or YPD plus 2.2 M sorbitol. Osmosensitive mutants lead to the formation of smaller colonies when grown on sorbitol-containing medium. The screen was performed twice by using an automated system, and a total of 179 mutants were scored as osmosensitive in both cases. In addition, we also scored the mutant cells for defective expression of an osmostress gene reporter system (STL1::LacZ) to link specific mutations to regulation of gene expression (not shown). Some of the mutants identified were already known as important genes for the response to osmostress (e.g., HOG1, PBS2, and GPD1 genes). Analysis of this large-scale data set was performed using the Internet-based tool "FunSpec" (http:\\funspec.med.utoronto.ca), which identified protein complexes enriched on the list of osmosensitive mutant strains (25). As shown in Table 1, several complexes without a previously defined role in the osmostress response were identified: protein complexes involved in different biological processes, such as cytoskeleton protein binding (Gim complexes), regulation of translation (mitochondrial processing complexes), and vacuole biogenesis (class C Vps protein complex). We also found different complexes related to regulation of gene expression that were required for cell viability upon high osmolarity: the previously characterized Rpd3 histone deacetylase complex (7) and two major transcriptional complexes, the SAGA and Mediator complexes.
|
|
It is known that, for instance, expression of STL1 and CTT1 depends on different transcription factors (i.e., Hot1 and Msn2/Msn4, respectively). To confirm that under severe stress conditions (1.2 M NaCl), expression of these genes is mediated by the known transcription factors, we tested STL1 and CTT1 gene expression in deficient hot1 and msn2 msn4 strains. Indeed, expression of STL1 and CTT1 also depends on Hot1 and Msn2/Msn4, respectively, in response to severe stress (Fig. 2). Therefore, SAGA is required under severe stress irrespective of the activator responsible for gene induction.
|
|
, med2, gal11, and srb4-1 mutants). As shown in Fig. 4A and B, mutant cells were sensitive to osmostress and already displayed a dramatic impairment of gene induction under mild osmotic conditions (0.4 M NaCl). Similar results were obtained with the SRB4-1 mutant (srb4ts), in which gene expression is dramatically affected at both 0.4 and 1.2 M NaCl (Fig. 4C and D). Thus, in contrast to the case with SAGA, the Mediator complex is fully required for Hog1-induced gene expression under any osmostress condition.
|
yeast strains expressing functional epitope-tagged Spt20 or Srb4 components of the SAGA and Mediator complexes from their natural locus were immunoprecipitated and analyzed by PCR. As shown in Fig. 5, Spt20, Srb4, and Pol II (Rpb1) were present at osmoresponsive genes only in response to osmostress, and their recruitment to osmostress promoters was completely dependent on Hog1. It is worth noting that binding of SAGA, Mediator, and Pol II occurred under mild and severe osmostress conditions (Fig. 5A and B). Thus, Hog1 is essential for the recruitment of SAGA, Mediator, and Pol II upon osmostress.
|
|
, spt20, and pgd1 yeast strains expressing functional epitope-tagged Hog1 from the natural locus was immunoprecipitated with antibodies against the hemagglutinin (HA) epitope and analyzed by PCR. As shown in Fig. 7A, binding of Hog1 to the STL1 promoter in response to mild osmostress conditions was abolished by deletion of HOT1, which encodes the transcription factor that mediates STL1 expression upon stress (2), whereas it was not affected by deletion of SPT20 or PGD1 (left panel). Similar results were obtained when binding of Hog1 was analyzed under severe osmostress conditions (right panel). This indicates that Hog1 recruitment to osmostress promoters is independent of SAGA and Mediator, and it is consistent with the previous observation that binding of Hog1 precedes binding of the two complexes at the promoters and the fact that Hog1 is essential for their recruitment (Fig. 5 and 6).
|
, and sin4 strains and analyzed binding of Srb4 to wild-type and spt20 strains. ChIP analyses showed that binding of the SAGA subunit Spt20 to STL1 upon osmostress was independent of the presence of Mediator under either mild or severe stress conditions (Fig. 7B and C). Similar results were observed for Ada2 (data not shown). Interestingly, although binding of the Srb4 Mediator subunit to STL1 was almost identical for wild-type and spt20 strains under mild osmostress (0.4 M NaCl), binding of Srb4 was significantly reduced in the spt20 cells where they were exposed to severe osmostress (1.2 M NaCl) (Fig. 7B and C). Therefore, in addition to the requirement of the Hog1 MAPK for binding, SAGA is required for efficient recruitment of Mediator under severe stress conditions.
Recently it was reported that Hog1 is recruited to coding regions of stress-responsive genes upon activation (20). In addition, recent reports have shown that Mediator is present on many coding regions of actively transcribed genes (3, 8). Global ChIP studies have shown that the SAGA subunit Gcn5 seems to be enriched on the ORFs of transcribing genes, although to a lesser extent than in promoters (24). Interestingly, a recent report has shown that several SAGA subunits are present on the GAL1 ORF upon galactose induction and on the ARG1 and ARG4 ORFs in response to amino acid deprivation (10). We have followed binding of Mediator and SAGA by ChIP analyses and found that under mild and severe osmostress conditions, both complexes are recruited to the coding region of STL1 (Fig. 8A and B). Under the same conditions, binding of Tbp1 is restricted to promoters (Fig. 8C). It is worth noting that binding of Mediator to the STL1 ORF is reduced in an spt20 strain under severe osmostress conditions, which is consistent with the diminished recruitment observed at the promoter (Fig. 7C and 8B).
|
Binding of Hog1 to Mediator is reduced in SAGA-deficient cells.
SAGA is recruited to different promoters through association to specific activators (27). We next tested whether Hog1 was able to interact with the SAGA complex by performing GST pull-down experiments with extracts from osmotically stressed cells expressing GST-Hog1 and chromosomally TAP-tagged versions of Ada2, Ada1, Spt7, Spt20, Spt3, and Spt8. In all cases, GST-Hog1 but not the GST control coprecipitated the TAP-tagged SAGA component (Fig. 9A). To analyze whether interaction of Hog1 with SAGA was mediated by the Mediator, we performed GST pull-down experiments with extracts from wild-type and pgd1 strains expressing GST-Hog1 and chromosomally HA-tagged Spt20. Hog1 coprecipitated Spt20 similarly with the two strains (Fig. 9B). Therefore, these results indicate that Hog1 associates with the SAGA complex and this association is independent of the presence of Mediator, which is in agreement with the ChIP data.
|
strains at 0.4 M and 1.2 M NaCl. Indeed, binding of Mediator to Hog1 is not affected by deletion of spt20 under mild osmostress conditions (0.4 M NaCl), but it is dramatically reduced under severe osmotic conditions (1.2 M NaCl) (Fig. 9C). Gel filtration analyses showed that under severe stress conditions, the integrity of the Mediator complex in a SAGA mutant is maintained (Fig. 10A). It is worth noting that SAGA and Mediator still interact under severe stress conditions, and this interaction does not seem to be affected by deletion of HOG1 (Fig. 10C). Thus, taken together, we propose that SAGA is critical in promoting the interaction of Mediator with Hog1 under severe osmostress conditions.
|
Thus, we initially tested binding of Pol II (Rpb1) to osmoresponsive promoters by ChIP in gal11, pgd1, and srb4-1 strains. As expected, binding of Pol II to STL1 and GRE2 was severely impaired even under mild osmostress conditions in Mediator mutant cells (Fig. 11A; also data not shown). We then performed a time course analysis of the recruitment of Pol II to osmostress promoters with a wild-type strain and a SAGA-deficient (spt20) strain under mild and severe osmostress conditions. In contrast to the requirement for Mediator, recruitment of Pol II was strongly dependent on the strength of the osmotic conditions. In a SAGA mutant strain, binding of polymerase to STL1 was only delayed under mild stress (0.4 M NaCl), whereas it was dramatically impaired when cells were subjected to 1.2 M NaCl (Fig. 11B and C). Correspondingly, binding of Tbp1 was also impaired under severe osmostress conditions in a SAGA-deficient mutant (Fig. 11D). Thus, whereas Mediator is essential to making possible Pol II recruitment upon stress, SAGA is required for Pol II recruitment and gene expression selectively under severe osmostress conditions.
|
|
DISCUSSION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
SAGA is a multisubunit protein complex involved in several aspects of transcription, for instance, TATA-binding protein delivery. SAGA and TFIID both act as important transcriptional coactivators that share a common set of subunits, although they seem to regulate different classes of genes. Actually, in a genome-wide analysis, it was shown that whereas TFIID function was important for transcription of about 90% of all yeast genes in the whole genome, only 10% seemed to be dependent on SAGA. Interestingly, SAGA-regulated genes were involved in a number of stress responses, and it was suggested that SAGA might be particularly geared for tuning on genes that respond to stress (13). Correspondingly, we found that whereas SAGA was important for proper osmostress responses, elimination of TAF1 or TAF2 (components of TFIID) did not affect stress genes, supporting the hypothesis of SAGA playing a specialized role in stress responses.
SAGA contains a number of components with specific catalytic activities; for instance, Gcn5 has histone acetylase activity, and Ubp8 plays a critical role in deubiquitination of H2B. Nevertheless, deletion of genes encoding these activities of SAGA has a more limited impact on global gene expression than deletion of central structural components of SAGA, such as SPT3 (13). Systematic analysis of the osmostress responses in the mutants whose mutations correspond to the components of SAGA has shown that the structural entity of SAGA, rather than specific catalytic activities, is important for gene expression and survival upon stress.
It is worth noting that deletion of SPT8 results in a phenotype similar to that with deletion of other SAGA subunits, which suggests that it is SAGA and not SALSA which is important for gene expression upon stress (data not shown).
Full Hog1-mediated transcriptional responses to osmostress require expression of genes under control of several transcription factors. Previous results showed that at least in Sko1-dependent genes, recruitment of SAGA was observed upon gene activation (22). However, the relevance of SAGA in osmostress transcription and how it was targeted to the osmostress promoters remained unclear. We have shown that SAGA is recruited to genes controlled by Sko1 but also by other transcription factors, such as Hot1 or Msn2 and Msn4. Thus, SAGA is important for expression of osmostress genes independently of the activator present on the promoter. It is worth noting that Hog1 is recruited to stress promoters upon stress (2), and once bound to osmoresponsive promoters, Hog1 acts as a transcriptional activator (1). ChIP analyses have shown that recruitment of Hog1 precedes and is independent of SAGA and Mediator, whereas recruitment of both complexes depends on Hog1. Correspondingly, Hog1 is able to coprecipitate with both SAGA and Mediator.
Recently it was shown that in addition to binding to osmostress promoters, Hog1 is also present on the coding regions of stress genes (20). The fact that Hog1 coprecipitates with and mediates recruitment of SAGA and Mediator suggested that binding of these complexes might not be limited to promoters. ChIP analyses have shown that indeed binding of SAGA and Mediator also occurs at the coding regions of osmostress genes. Along these lines, recent reports have shown that Mediator and SAGA are present on many coding regions of actively transcribed genes (8, 10, 3).
The Mediator complex plays an important role as a transcriptional coactivator (14). Actually, inactivation of some of the subunits of Mediator, such as Srb4 (Med17), affects cell survival as a result of a global decrease in gene expression (12). Inactivation of other subunits has a much less dramatic effect. Here we show that deletion of nonessential components of Mediator results in cells with compromised survival upon osmostress and with a dramatic decrease of expression of osmoresponsive genes. Furthermore, Mediator is recruited to osmostress promoters upon induction (as reported previously [8]), and its recruitment is dependent on Hog1. The crucial relevance of Mediator in osmostress is illustrated by the fact that cells become osmosensitive even under mild stress conditions (data not shown).
The Mediator complex seems to be essential under both mild and severe stress conditions, whereas SAGA seems to be essential only under severe osmostress conditions. It is worth noting that SAGA is recruited under both mild and severe osmostress, and although it is essential only for cell survival under severe stress, the lack of SAGA already alters the normal pattern of gene expression at mild osmolarity. Thus, both SAGA and Mediator are recruited similarly to stress genes, and their recruitment depends on Hog1. Interestingly, although binding of SAGA is always observed upon osmostress independently of Mediator, binding of Mediator is reduced in a SAGA mutant strain under severe osmostress conditions. It is worth noting that SAGA and Mediator are able to interact under severe osmostress conditions, and this binding seem to be independent of Hog1. Taken together, we propose the following mechanism for the role of SAGA and Mediator in osmostress gene expression. Recruitment of Hog1 to promoters stimulates binding of SAGA and Mediator to promoters. Under mild stress conditions, there should be a redundant mechanism that leads to the recruitment of Mediator, both dependent on and independent of SAGA (possibly by direct binding with Pol II). Under severe stress conditions, SAGA provides the unique route that makes possible the recruitment of Mediator, which suggests that binding of Hog1 to Mediator is indirect and is mediated by SAGA, at least under severe osmostress. Under these conditions, the lack of SAGA reduces the amount of Mediator recruited to the promoters, Pol II recruitment is affected, and thus, transcription is strongly impaired. Consistent with this model, binding of Mediator to Hog1 is strongly reduced in cells deficient in SAGA only under severe stress conditions.
Thus, our results define an essential role for Mediator in osmostress gene expression and a selective role for SAGA under severe osmolarity conditions. In addition, our results indicate that the requirement for a transcriptional complex for the expression of a given promoter might be fine-tuned according to the strength of the stimuli perceived by the cell through the regulation of the interactions between transcriptional complexes.
|
ACKNOWLEDGMENTS |
|---|
M.Z. is the recipient of a Ramón Areces Ph.D. fellowship. This work was supported by grants from Ministerio de Educación y Ciencia, from the European Science Foundation (ESF) under the EUROCORES Program EuroDYNA, through contract no. ERAS-CT-2003-980409 of the European Commission, DG Research, FP6, and as part of a EURYI scheme award (www.esf.org/euryi) to F.P. and a grant from Ministerio de Educación y Ciencia to E.D.N.
|
FOOTNOTES |
|---|
Published ahead of print on 2 April 2007.
|
REFERENCES |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
2. Alepuz, P. M., A. Jovanovic, V. Reiser, and G. Ammerer. 2001. Stress-induced map kinase Hog1 is part of transcription activation complexes. Mol. Cell 7:767-777.[CrossRef][Medline]
3. Andrau, J. C., L. van de Pasch, P. Lijnzaad, T. Bijma, M. G. Koerkamp, J. van de Peppel, M. Werner, and F. C. Holstege. 2006. Genome-wide location of the coactivator mediator: binding without activation and transient Cdk8 interaction on DNA. Mol. Cell 22:179-192.[CrossRef][Medline]
4. Bryant, G. O., and M. Ptashne. 2003. Independent recruitment in vivo by Gal4 of two complexes required for transcription. Mol. Cell 11:1301-1309.[CrossRef][Medline]
5. de Nadal, E., P. M. Alepuz, and F. Posas. 2002. Dealing with osmostress through MAP kinase activation. EMBO Rep. 3:735-740.[CrossRef][Medline]
6. de Nadal, E., L. Casadome, and F. Posas. 2003. Targeting the MEF2-like transcription factor Smp1 by the stress-activated Hog1 mitogen-activated protein kinase. Mol. Cell. Biol. 23:229-237.
7. de Nadal, E., M. Zapater, P. M. Alepuz, L. Sumoy, G. Mas, and F. Posas. 2004. The MAPK Hog1 recruits Rpd3 histone deacetylase to activate osmoresponsive genes. Nature 427:370-374.[CrossRef][Medline]
8. Fan, X., D. M. Chou, and K. Struhl. 2006. Activator-specific recruitment of Mediator in vivo. Nat. Struct. Mol. Biol. 13:117-120.[CrossRef][Medline]
9. Govind, C. K., S. Yoon, H. Qiu, S. Govind, and A. G. Hinnebusch. 2005. Simultaneous recruitment of coactivators by Gcn4p stimulates multiple steps of transcription in vivo. Mol. Cell. Biol. 25:5626-5638.
10. Govind, C. K., F. Zhang, H. Qiu, K. Hofmeyer, and A. G. Hinnebusch. 2007. Gcn5 promotes acetylation, eviction, and methylation of nucleosomes in transcribed coding regions. Mol. Cell 25:31-42.[CrossRef][Medline]
11. Hohmann, S. 2002. Osmotic stress signaling and osmoadaptation in yeasts. Microbiol. Mol. Biol. Rev. 66:300-372.
12. Holstege, F. C., E. G. Jennings, J. J. Wyrick, T. I. Lee, C. J. Hengartner, M. R. Green, T. R. Golub, E. S. Lander, and R. A. Young. 1998. Dissecting the regulatory circuitry of a eukaryotic genome. Cell 95:717-728.[CrossRef][Medline]
13. Huisinga, K. L., and B. F. Pugh. 2004. A genome-wide housekeeping role for TFIID and a highly regulated stress-related role for SAGA in Saccharomyces cerevisiae. Mol. Cell 13:573-585.[CrossRef][Medline]
14. Kornberg, R. D. 2005. Mediator and the mechanism of transcriptional activation. Trends Biochem. Sci. 30:235-239.[CrossRef][Medline]
15. Kuras, L., and K. Struhl. 1999. Binding of TBP to promoters in vivo is stimulated by activators and requires Pol II holoenzyme. Nature 399:609-613.[CrossRef][Medline]
16. Kyriakis, J. M., and J. Avruch. 2001. Mammalian mitogen-activated protein kinase signal transduction pathways activated by stress and inflammation. Physiol. Rev. 81:807-869.
17. Lee, T. I., H. C. Causton, F. C. Holstege, W. C. Shen, N. Hannett, E. G. Jennings, F. Winston, M. R. Green, and R. A. Young. 2000. Redundant roles for the TFIID and SAGA complexes in global transcription. Nature 405:701-704.[CrossRef][Medline]
18. Li, B., and J. C. Reese. 2000. Derepression of DNA damage-regulated genes requires yeast TAF(II)s. EMBO J. 19:4091-4100.[CrossRef][Medline]
19. Nehlin, J. O., M. Carlberg, and H. Ronne. 1992. Yeast SKO1 gene encodes a bZIP protein that binds to the CRE motif and acts as a repressor of transcription. Nucleic Acids Res. 20:5271-5278.
20. Proft, M., G. Mas, E. de Nadal, A. Vendrell, N. Noriega, K. Struhl, and F. Posas. 2006. The stress-activated hog1 kinase is a selective transcriptional elongation factor for genes responding to osmotic stress. Mol. Cell 23:241-250.[CrossRef][Medline]
21. Proft, M., A. Pascual-Ahuir, E. de Nadal, J. Arino, R. Serrano, and F. Posas. 2001. Regulation of the Sko1 transcriptional repressor by the Hog1 MAP kinase in response to osmotic stress. EMBO J. 20:1123-1133.[CrossRef][Medline]
22. Proft, M., and K. Struhl. 2002. Hog1 kinase converts the Sko1-Cyc8-Tup1 repressor complex into an activator that recruits SAGA and SWI/SNF in response to osmotic stress. Mol. Cell 9:1307-1317.[CrossRef][Medline]
23. Proft, M., and K. Struhl. 2004. MAP kinase-mediated stress relief that precedes and regulates the timing of transcriptional induction. Cell 118:351-361.[CrossRef][Medline]
24. Robert, F., D. K. Pokholok, N. M. Hannett, N. J. Rinaldi, M. Chandy, A. Rolfe, J. L. Workman, D. K. Gifford, and R. A. Young. 2004. Global position and recruitment of HATs and HDACs in the yeast genome. Mol. Cell 16:199-209.[CrossRef][Medline]
25. Robinson, M. D., J. Grigull, N. Mohammad, and T. R. Hughes. 2002. FunSpec: a web-based cluster interpreter for yeast. BMC Bioinform. 3:35.[CrossRef][Medline]
26. Sheikh-Hamad, D., and M. C. Gustin. 2004. MAP kinases and the adaptive response to hypertonicity: functional preservation from yeast to mammals. Am. J. Physiol. Renal Physiol. 287:F1102-F1110.
27. Timmers, H. T., and L. Tora. 2005. SAGA unveiled. Trends Biochem. Sci. 30:7-10.[CrossRef][Medline]
28. Tong, A. H., M. Evangelista, A. B. Parsons, H. Xu, G. D. Bader, N. Page, M. Robinson, S. Raghibizadeh, C. W. Hogue, H. Bussey, B. Andrews, M. Tyers, and C. Boone. 2001. Systematic genetic analysis with ordered arrays of yeast deletion mutants. Science 294:2364-2368.
29. Vincent, A. C., and K. Struhl. 1992. ACR1, a yeast ATF/CREB repressor. Mol. Cell. Biol. 12:5394-5405.
30. Westfall, P. J., D. R. Ballon, and J. Thorner. 2004. When the stress of your environment makes you go HOG wild. Science 306:1511-1512.
31. Wu, P. Y., C. Ruhlmann, F. Winston, and P. Schultz. 2004. Molecular architecture of the S. cerevisiae SAGA complex. Mol. Cell 15:199-208.[CrossRef][Medline]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| J. Bacteriol. | J. Virol. | Eukaryot. Cell |
|---|
| Microbiol. Mol. Biol. Rev. | Clin. Vaccine Immunol. | All ASM Journals |
|---|
