![[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}
Laboratory of Molecular Growth Regulation,1 Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, Bethesda, Maryland,2 Laboratory of Genetics, National Institute on Aging, Baltimore, Maryland3
Received 15 September 2005/ Returned for modification 31 October 2005/ Accepted 18 November 2005
 |
ABSTRACT |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
INTRODUCTION |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Vertebrate La proteins can modulate the translation of mRNAs that contain internal ribosome entry sites, as well as mRNAs that contain 5'-terminal oligopyrimidine motifs that encode ribosome subunits and translation factors (8, 28; reviewed in reference 33). The association of human Mdm2 mRNA with La promotes MDM2 translation with consequent decrease in p53 protein level and leukemia progression (31). La is also found associated with mRNAs in Saccharomyces cerevisiae, including mRNAs that encode ribosome subunits (14). Deletion of La from yeasts leads to alterations in the maturation pathways of pre-tRNAs (2, 5, 6, 16, 17, 26, 35) and pre-snoRNAs involved in rRNA biogenesis (14, 21). Thus, it was surprising that La is nonessential in yeasts, except when tRNAs or RNA-associated factors acquire debilitating mutations (21, 29, 33) and upon a conditional induction of the unfolded protein response (14).
The conserved N-terminal domain of La is comprised of a La motif and RNA recognition motif (RRM) that cooperate for high-affinity 3' UUU-OH binding (1, 9, 18). However, while these motifs constitute the La proteins of yeasts, metazoan La proteins also contain another, atypical RRM in their C termini (18).
In the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe, the organisms in which La has been characterized most extensively, La is dispensable. Small-interfering-RNA-mediated knockdown of La modestly decreased HeLa cell survival but was associated with more significant growth defects in the protozoan Trypanosoma brucei (10, 32). A genetic analysis suggested that La is required during a late (larval) stage of development in Drosophila melanogaster (3). While the La protein of humans (hLa) differs in length and sequence from those of D. melanogaster, T. brucei, and yeasts (<34%, <28%, and <24% identity with hLa, respectively), it is most highly homologous to mouse La (mLa) in overall structure and sequence (76% identity) (22). Yet, although much has been learned about hLa using heterologous systems and from in vitro analyses (15, 16, 18, 21, 33), there has been relatively very little analysis of La function in a mammal. A question that remained was whether La is essential in mammals and if so, at what developmental stage. To explore this, we created a disrupted La gene in mice and analyzed its effects on mouse development and the establishment of embryonic stem (ES) cells in vitro. The results demonstrated that, in contrast to yeasts, La is required in mammals as early as blastocyst development.
|
MATERIALS AND METHODS |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
Preimplantation embryos were flushed from uteri, and individual embryos were incubated overnight at 55°C in 15 µl of embryo lysis buffer (50 mM KCl, 10 mM Tris-HCl, pH 8, 2 mM MgCl2, 0.45% Nonidet P-40 [NP-40], 0.45% Tween 20, and 0.1 mg/ml proteinase K). The proteinase was then inactivated by incubation at 100°C for 2 min, and 8-µl samples of the lysed embryos were added to 17 µl of PCR master mix containing 10x PCR buffer, primer, deoxynucleoside triphosphates, and Taq polymerase (BD Biosciences). PCR mixtures were heated at 94°C for 1 min and then subjected to 35 cycles, with 1 cycle consisting of 94°C for 45 s and 68°C for 2 min.
Southern and Northern blotting.
DNA obtained from
the livers of La+/+ and
La+/– mice was digested
with AflIII, EcoRI, or HindIII, separated on 0.9% agarose gel,
denatured, and transferred to a nylon membrane (GeneScreen Plus;
Perkin-Elmer Life Sciences). Probes for Southern analysis were derived
from mLa gene intron 2 and the Neo gene as indicated in Fig.
2A. Probes were labeled by
random priming with [
-32P]dCTP (Lofstrand Labs,
Gaithersburg, MD). Hybridization was in QuikHyb solution processed
accordingly (Stratagene). The membrane was exposed to a Fuji
phosphorimager screen and analyzed using Image Gauge
software.
Adult mouse multiple tissue and mouse embryo Northern
blots were obtained from Clontech. Full-length mLa and beta-actin cDNAs
were labeled by random priming with [-32P]dCTP. For
La+/+ and
La+/– samples, total RNA
was prepared from tissue dissected from adult littermates using TRIzol
(Invitrogen), and 30 µg was electrophoresed and transferred to
a charged nylon membrane (GeneScreen Plus; Perkin-Elmer Life
Sciences, Inc.). Blots were probed first with a radiolabeled 0.7-kb
3' fragment of mLa cDNA followed by beta-actin cDNA.
Hybridization was performed as described above for Southern
blotting.
Cloning, expression, and purification of His-tagged recombinant mLa antigen and affinity purification of anti-mLa Ab. mLa cDNA (30) was modified to encode a C-terminal His6 tag and cloned into the NcoI-XhoI fragment of pET-28a (Novagen). After 4 h of induction by isopropyl-ß-D-thiogalactopyranoside (IPTG), purification was performed by nickel-agarose chromatography (QIAGEN). Anti-mLa serum was obtained from a rabbit immunized with purified recombinant mLa. For affinity purification, a preparative sodium dodecyl sulfate gel containing purified recombinant mLa was electroblotted onto a nitrocellulose strip, and the band corresponding to full-length mLa was cut out and used as an affinity matrix (25). Briefly, the nitrocellulose strips were washed with 100 mM glycine-HCl, pH 2.5, and then with phosphate-buffered saline (PBS) containing 0.05% NP-40, blocked with 5% bovine serum albumin in PBS, and incubated with anti-mLa serum for 3 h at room temperature. The strips were washed, eluted with 100 mM glycine-HCl (pH 2.5), and neutralized with Tris base to pH 7.5. The concentration of the affinity-purified antibody (Ab) was determined by comparison to the concentration of purified rabbit immunoglobulin G (IgG) (Zymed Labs, Inc.) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Coomassie blue staining.
Immunoblot analysis. Liver and 32D cells were washed once with ice-cold PBS containing 1 mM phenylmethanesulfonyl fluoride (PMSF), and lysed in ice-cold lysis buffer containing 1% NP-40, 0.5 M NaCl, 10 mM HEPES, pH 7.5, 10% glycerol, 1 mM PMSF, and complete protease inhibitor cocktail (Roche). The liver was homogenized on ice with a Brinkmann polytron (Kinematica) and sonicated on ice with an XL-2020 sonicator (Misonix) equipped with a Misonix microtip probe 419 (3.2-mm tip diameter; 16.5-cm length) at 550 W; the liver was sonicated three times for 10 s each time. The samples were then rocked gently for 30 min at 4°C and cleared by centrifugation at 15,000 x g for 10 min. Extraction of 32D cells was the same except without polytron homogenization. Protein quantitation was performed by using Bio-Rad protein reagent. Cleared lysates (50 µg) were separated on a precast 12% Tris-glycine polyacrylamide gel (Invitrogen) and transferred to a nitrocellulose membrane. The membrane was incubated with anti-mLa serum or affinity-purified anti-mLa and visualized with 125I-protein A (Amersham Biosciences).
Blastocyst outgrowth, immunofluorescence (IF), and genotyping. Blastocysts were recovered at 3.5 days postcoitus and cultured individually in Dulbecco's modified Eagle's medium (Gibco catalog no. 10313-021) supplemented with 15% ES cell-certified fetal bovine serum, 15 mM HEPES buffer, 100 units/ml of penicillin, 100 µg/ml of streptomycin, 100 µM nonessential amino acids, 4.5 mM of L-glutamine, and 100 µM of ß-mercaptoethanol on gelatinized chamber slides (Nalge Nunc International) at 37°C in 5% CO2. The blastocysts were visualized using an Olympus LH50A microscope equipped with a Polaroid DMC Ie digital camera. The chamber slides were incubated in 4% paraformaldehyde in PBS for 30 min and washed in PBS, and the embryos were permeabilized and fixed with 100% methanol for 20 min, washed, and blocked with PBS containing 3% bovine serum albumin and 0.1% Tween 20 for 30 min. The embryos were then washed and incubated with TROMA-I antibody (Developmental Studies Hybridoma Bank) at 1:25 in the blocking solution overnight at 4°C. The embryos were washed and incubated with Texas red-conjugated goat anti-rat IgG (1:200 in blocking solution; Vector Laboratories). The embryos were then washed, incubated in 0.5 µg/ml of purified anti-mLa antibody in blocking solution overnight at 4°C, washed, incubated with FITC-conjugated goat anti-rabbit IgG (1:200 in blocking solution), and washed. The embryos were then mounted on slides in SlowFade Light Antifade medium with 4',6'-diamidino-2-phenylindole (DAPI) (1.5 µg/ml; Molecular Probes) and observed with a Nikon Eclipse E600 microscope equipped with a Nikon digital camera DXM1200F, using ACT-1 and Adobe software. For genotyping, individual embryos were recovered from the slides, transferred to PCR tubes, and processed as described above.
ES cell lines. Embryonic stage E3.5 (embryonic day 3.5) blastocysts were isolated and cultured on mitomycin C-treated mouse embryonic fibroblasts in Dulbecco's modified Eagle's medium (Gibco catalog no. 10313-021) for 4 days as described previously (24, 27). The inner cell mass (ICM) was picked, trypsinized, replated, and cultured for 7 days. Undifferentiated ES cell colonies were picked, trypsinized, and expanded.
|
RESULTS |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-amanitin suggested that the La
mRNA observed prior to the four-cell stage was largely due to maternal
stores (data not shown). These results revealed that La mRNA is
ubiquitously expressed throughout mouse development and in the adult
animal.
|
Several preimplantation embryos collected at E3.5 appeared at the morula and blastocyst stages, as represented in Fig. 1E. In Fig. 1E, panels a to c and g to i reveal immunofluorescence using affinity-purified anti-mLa, while panels d to f and j to l used antiactin as a control. mLa was readily detected in the samples shown and in all other preimplantation embryos examined (not shown). mLa was predominantly nuclear as expected, although cytoplasmic staining also seemed apparent, albeit to a lesser degree, most notably in cells of the ICM (Fig. 1E, panel g). These results confirmed that embryo stages in which mLa mRNA was detected by microarray also produced mLa protein.
Disrupting the La gene in mice. A vector targeting homologous recombination was introduced into mice in which the first two exons of the mLa gene (the second of which contained the initiation AUG) were replaced by a neomycin resistance cassette (Fig. 2A). Germ line transmission of the disrupted allele was confirmed by PCR genotyping of offspring (Fig. 2B). The presence of the PCR band of the expected size from the disrupted allele reflects correct targeting, since one of the primers was outside the targeting vector.
Restriction analysis by Southern blotting with a probe derived from intron 2 of the mLa gene confirmed the targeted locus in La+/– offspring (Fig. 2C). Since the mLa intron probe used is fully represented in the targeting vector, the absence of unexpected additional bands in the La+/– offspring provides evidence that the targeting vector was limited to insertion at the La locus only (Fig. 2C, top panels). Stripping followed by reprobing of the same blot using a probe derived from the Neo cassette revealed only bands of the size predicted for insertion at the La locus with no evidence of additional insertions (Fig. 2C). The PCR and Southern blot data allow the conclusion that the mLa gene was correctly targeted as indicated in Fig. 2A.
La is essential in mice, and haploinsufficiency leads to reduced La mRNA levels. PCR genotyping of pups from La+/– intercrosses revealed no La–/– offspring detected(Table 1).Thorough pathological examination of several La+/– heterozygotes revealed no abnormalities compared to a control La+/+ group (data not shown). Although the La+/– miceexhibited no overt phenotype, their mRNA levels were examined nevertheless. RNA isolated from three different tissues from each of five La+/– and La+/+ mice were examined by Northern blotting, quantitated, and normalized to beta-actin mRNA (Fig. 3A). La mRNA levels in La+/– mice were reduced to 60 to 70% of the level in La+/+ mice (Fig. 3B).
|
|
We next analyzed preimplantation embryos from La+/– intercrosses. The PCR genotyping data obtained from a small sample of preimplantation embryos is shown in Fig. 4A. Among 80 preimplantation morulae and blastocysts examined, 23 were found to be La–/–, reflecting the expected Mendelian inheritance pattern (Table 1). These data indicate that La–/– embryos did not survive beyond the blastocyst stage.
|
The La+/– and La+/+ ES cell lines were examined for mLa expression. Whole-cell extracts from several of the ES lines, each derived from an independent blastocyst, were examined by immunoblotting and compared to HSP90 (and other controls, not shown) on the same blot (Fig. 4C). A variable amount of a minor band that migrated below the major La band that presumably represents a degradation product was visible in both the La+/+ and La+/– ES cell extracts (Fig. 4C and data not shown). La+/– cells expressed about 60% as much mLa protein as La+/+ cells did (Fig. 4C and D). These data indicate that La is expressed in ES cells in a gene dose-dependent manner and is required for ES cell development.
mLa is required for maintenance of the inner cell mass in vitro. The requirement of La protein for ES cell development suggested that La was required for maintenance of the ICM. To test this hypothesis, blastocysts isolated at E3.5 were cultured in plastic dishes in vitro, subjected to IF, and genotyped. All of the blastocysts hatched from the zona pellucida and attached to the substratum, their ICMs began to expand, and outgrowths of migrating trophoblast cells started to form by day 3, as exemplified by the three samples shown in Fig. 5A. In contrast to the La+/+ and La+/– blastocysts, the ICMs of the La–/– blastocysts began to decrease in mass after day 3 (Fig. 5A and B). ICM loss from the nullizygotes became manifest over the next 3 days, whereas the trophoblast cells as evidenced by their cell type-specific protein TROMA-I (4) persisted (Fig. 5A to D and data not shown). Moreover, nuclei in trophoblast giant cells derived from La–/– blastocysts appeared consistently smaller than those derived from La+/+ and La+/– blastocysts. La–/– blastocysts appeared to degenerate by 10 days in culture (Fig. 5C).
|
|
DISCUSSION |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
On the basis of the expression profile for La during mouse development, which reflects activation between the four- and eight-cell stage (Fig. 1C), La can be assigned to the mid-preimplantation gene activation group of early embryonic expressed genes, which is consistent with the absence of an effect by alpha-amanitin (12). Microarray data (not shown) revealed that cycloheximide significantly increased the expression of La mRNA. This suggests that the degradation of maternally stored La mRNA is facilitated by a protein that is synthesized after fertilization, similar to other genes showing this expression pattern (12).
As with any targeting strategy, the possibility that another chromosomal locus was disrupted existed. However, since the probe used for Southern blot analysis is fully represented in the targeting vector, the absence of unexpected additional bands in the La+/– offspring provides evidence that the targeting vector was limited to the La locus (Fig. 2C). Likewise, a probe derived from the Neo cassette did not reveal insertions other than at a single La locus (Fig. 2C). Thus, as best as can be determined, the targeting vector appears not to have inserted anywhere other than at the La locus, as designed.
The La+/– mice developed normally although they contained less mLa mRNA than La+/+ mice. We examined small RNAs that are known to be La associated in the La+/– and La+/+ ES cells. No significant differences were detected in the levels of the stable RNA polymerase III transcripts of mY3 RNA in the La+/+ and La+/– cells (not shown). Preliminary data suggest differences in the metabolism of certain pre-tRNAs in the La+/+ and La+/– ES cells (M. W. Bruinsma and R. J. Maraia, unpublished observations), although the significance of this remains to be determined. Future studies will also include characterization of mRNA differences in the La+/+ and La+/– ES cells.
Prior data provided evidence that La may be required for development in Drosophila melanogaster (3), albeit at a much later stage than observed in mice. As discussed in the introduction, yeast La is nonessential but is conditionally required for the unfolded protein response as well as when essential tRNA genes acquire debilitating mutations. The requirement for La during early mouse development may reflect the fact that metazoan La proteins contain an RRM in their C-terminal domain that is absent in yeasts (22, 33, 34).
In summary, we have shown that nullizygous disruption of the mouse La gene leads to early embryonic lethality, consistent with the observed critical defect in the ICM of the blastocyst observed during blastocyst outgrowth.
|
ACKNOWLEDGMENTS |
|---|
This research was supported by the Intramural Research Program of NICHD, NIH. R.J.M. is a Commissioned Officer in the U.S. Public Health Service.
|
FOOTNOTES |
|---|
|
REFERENCES |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
2. Anderson,
J., L. Phan, R. Cuesta, B. A. Carlson, M. Pak, K. Asano,
G. R. Bjork, M. Tamame, and A. G. Hinnebusch.1998
. The essential Gcd10p-Gcd14p nuclear complex is
required for 1-methyladenosine modification and maturation of initiator
methionyl-tRNA. Genes Dev.
12:3650-3662.
3. Bai,
C., and P. P. Tolias. 2000. Genetic analysis
of a La homolog in Drosophila melanogaster.Nucleic Acids Res.
28:1078-1084.
4. Brulet,
P., C. Babinet, R. Kemler, and F. Jacob. 1980.
Monoclonal antibodies against trophectoderm-specific markers during
mouse blastocyst formation. Proc. Natl. Acad. Sci. USA
77:4113-4117.
5. Calvo,
O., R. Cuesta, J. Anderson, N. Gutierrez, M. T.
Garcia-Barrio, A. G. Hinnebusch, and M. Tamame.1999
. GCD14p, a repressor of GCN4 translation,
cooperates with Gcd10p and Lhp1p in the maturation of initiator
methionyl-tRNA in Saccharomyces cerevisiae.Mol. Cell. Biol.
19:4167-4181.
6. Chakshusmathi, G., S. D. Kim, D. A. Rubinson, and S. L. Wolin. 2003. A La protein requirement for efficient pre-tRNA folding. EMBO J. 22:6562-6572.[CrossRef][Medline]
7. Chambers,
J. C., and J. D. Keene. 1985.
Isolation and analysis of cDNA clones expressing human lupus La
antigen. Proc. Natl. Acad. Sci. USA
82:2115-2119.
8. Costa-Mattioli,
M., Y. Svitkin, and N. Sonenberg. 2004. La autoantigen
is necessary for optimal function of the poliovirus and hepatitis C
virus internal ribosome entry site in vivo and in vitro. Mol.
Cell. Biol.
24:6861-6870.
9. Dong, G., G. Chakshusmathi, S. L. Wolin, and K. M. Reinisch. 2004. Structure of the La motif: a winged helix domain mediates RNA binding via a conserved aromatic patch.EMBO J. 23:1000-1007.[CrossRef][Medline]
10. Foldynova-Trantirkova, S., Z. Paris, N. R. Sturm, D. A. Campbell, and J. Lukes. 2005. The Trypanosoma brucei La protein is a candidate poly(U) shield that impacts spliced leader RNA maturation and tRNA intron removal. Int. J. Parasitol. 35:359-366.[CrossRef][Medline]
11. Habets, W. J., J. H. denBrok, A. M. Boerbooms, L. B. van de Putte, and W. J. van Venrooij.1983 . Characterization of the SS-B (La) antigen in adenovirus-infected and uninfected HeLa cells. EMBO J. 2:1625-1631.[Medline]
12. Hamatani, T., M. G. Carter, A. A. Sharov, and M. S. Ko. 2004. Dynamics of global gene expression changes during mouse preimplantation development. Dev. Cell 6:117-131.[CrossRef][Medline]
13. Hoch, S. O., and P. B. Billings. 1984. Characterization of the La (SS-B) antigen from several mammalian sources. J. Immunol. 133:1397-1403.[Abstract]
14. Inada,
M., and C. Guthrie. 2004. Identification of
Lhp1p-associated RNAs by microarray analysis in Saccharomyces
cerevisiae reveals association with coding and noncoding RNAs.Proc. Natl. Acad. Sci. USA
101:434-439.
15. Intine, R. V., M. Dundr, T. Misteli, and R. J. Maraia.2002 . Aberrant nuclear trafficking of La protein leads to disordered processing of associated precursor tRNAs. Mol. Cell 9:1113-1123.[CrossRef][Medline]
16. Intine, R. V. A., A. L. Sakulich, S. B. Koduru, Y. Huang, E. Pierstorrf, J. L. Goodier, L. Phan, and R. J. Maraia. 2000. Transfer RNA maturation is controlled by phosphorylation of the human La antigen on serine 366.Mol. Cell 6:339-348.[CrossRef][Medline]
17. Johansson, M. J., and A. S. Bystrom. 2002. Dual function of the tRNA(m(5)U54)methyltransferase in tRNA maturation.RNA 8:324-335.[Abstract]
18. Kenan, D. J., and J. D. Keene. 2004. La gets its wings. Nat. Struct. Mol. Biol. 11:303-305.[CrossRef][Medline]
19. Kohn,
M. J., S. W. Leung, V. Criniti, M. Agromayor, and
L. Yamasaki. 2004. Dp1 is largely dispensable for
embryonic development. Mol. Cell. Biol.
24:7197-7205.
20. Lerner,
M. R., J. A. Boyle, J. A. Hardin, and
J. A. Steitz. 1981. Two novel classes of
small ribonucleoproteins detected by antibodies associated with lupus
erythematosus. Science
211:400-402.
21. Maraia, R. J., and R. V. Intine. 2002. La protein and its associated small nuclear and nucleolar precursor RNAs.Gene Expr. 10:41-57.[Medline]
22. Maraia,
R. J., and R. V. Intine. 2001.
Recognition of nascent RNA by the human La antigen: conserved and
divergent features of structure and function. Mol. Cell.
Biol.
21:367-379.
23. Maraia,
R. J., D. J. Kenan, and J. D. Keene.1994
. Eukaryotic transcription termination factor La
mediates transcript release and facilitates reinitiation by RNA
polymerase III. Mol. Cell. Biol.
14:2147-2158.
24. Nagy, A., M. Gertsenstein, K. Vintersten, and R. Behringer.2003 . Manipulating the mouse embryo: a laboratory manual, 3rd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.
25. Olmsted,
J. B. 1981. Affinity purification of
antibodies from diazotized paper blots of heterogeneous protein
samples. J. Biol. Chem.
256:11955-11957.
26. Pannone, B., D. Xue, and S. L. Wolin. 1998. A role for the yeast La protein in U6 snRNP assembly: evidence that the La protein is a molecular chaperone for RNA polymerase III transcripts.EMBO J. 17:7442-7453.[CrossRef][Medline]
27. Robertson, E. J. (ed.). 1987. Teratocarcinomas and embryonic stem cells: a practical approach. IRL Press Ltd., Oxford, England.
28. Schwartz,
E., R. V. Intine, and R. J. Maraia.2004
. CK2 is responsible for phosphorylation of human La
protein serine-366 and can modulate rpL37 5'-terminal
oligopyrimidine mRNA metabolism. Mol. Cell. Biol.
24:9580-9591.
29. Stefano, J. E. 1984. Purified lupus antigen La recognizes an oligouridylate stretch common to the 3' termini of RNA polymerase III transcripts. Cell 36:145-154.[CrossRef][Medline]
30. Topfer, F., T. Gordon, and J. McCluskey. 1993. Characterization of the mouse autoantigen La (SS-B).J. Immunol. 150:3091-3100.[Abstract]
31. Trotta, R., T. Vignudelli, L. Pecorari, R. V. Intine, C. Guerzoni, G. Santilli, O. Candini, M. W. Byrom, S. Goldoni, L. P. Ford, M. A. Caligiuri, R. Maraia, D. Perrotti, and B. Calabretta. 2003. BCR/ABL activates mdm2 mRNA translation via the La antigen. Cancer Cell 3:145-160.[CrossRef][Medline]
32. Watkins, N. J., I. Lemm, D. Ingelfinger, C. Schneider, M. Hossbach, H. Urlaub, and R. Luhrmann. 2004. Assembly and maturation of the U3 snoRNP in the nucleoplasm in a large dynamic multiprotein complex. Mol. Cell 16:789-798.[CrossRef][Medline]
33. Wolin, S. L., and T. Cedervall. 2002. The La protein. Annu. Rev. Biochem. 71:375-403.[CrossRef][Medline]
34. Yoo,
C. J., and S. L. Wolin. 1994. La
proteins from Drosophila melanogaster and
Saccharomyces cerevisiae: a yeast homolog of the La
autoantigen is dispensable for growth. Mol. Cell. Biol.
14:5412-5424.
35. Yoo, C. J., and S. L. Wolin. 1997. The yeast La protein is required for the 3' endonucleolytic cleavage that matures tRNA precursors. Cell 89:393-402.[CrossRef][Medline]
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| J. Bacteriol. | J. Virol. | Eukaryot. Cell |
|---|
| Microbiol. Mol. Biol. Rev. | Clin. Vaccine Immunol. | All ASM Journals |
|---|
