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Molecular and Cellular Biology, February 2008, p. 1361-1372, Vol. 28, No. 4
0270-7306/08/$08.00+0     doi:10.1128/MCB.01291-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Slx5 Promotes Transcriptional Silencing and Is Required for Robust Growth in the Absence of Sir2{triangledown} ,{dagger}

Russell P. Darst, Sandra N. Garcia,{ddagger} Melissa R. Koch, and Lorraine Pillus*

Section of Molecular Biology, Division of Biological Sciences, UCSD Moores Cancer Center, University of California, San Diego, La Jolla, California 92093-0347

Received 18 July 2007/ Returned for modification 9 August 2007/ Accepted 5 December 2007

The broadly conserved Sir2 NAD+-dependent deacetylase is required for chromatin silencing. Here we report the discovery of physical and functional links between Sir2 and Slx5 (Hex3), a RING domain protein and subunit of the Slx5/8 complex column, which is a ubiquitin E3 ligase that targets sumoylated proteins. Slx5 interacted with Sir2 by two-hybrid and glutathione S-transferase-binding assays and was found to promote silencing of genes at telomeric or ribosomal DNA (rDNA) loci. However, deletion of SLX5 had no detectable effect on the distribution of silent chromatin components and only slightly altered the deacetylation of histone H4 lysine 16 at the telomere. In vivo assays indicated that Sir2-dependent silencing was functionally intact in the absence of Slx5. Although no previous reports suggest that Sir2 contributes to the fitness of yeast populations, we found that Sir2 was required for maximal growth in slx5{Delta} mutant cells. A similar requirement was observed for mutants of the SUMO isopeptidase Ulp2/Smt4. The contribution of Sir2 to optimal growth was not due to known Sir2 roles in mating-type determination or rDNA maintenance but was connected to a role of sumoylation in transcriptional silencing. These results indicate that Sir2 and Slx5 jointly contribute to transcriptional silencing and robust cellular growth.

* Corresponding author. Mailing address: Department of Molecular Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0347. Phone: (858) 822-2442. Fax: (858) 534-0555. E-mail: lpillus{at}ucsd.edu

{triangledown} Published ahead of print on 17 December 2007.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{ddagger} Present address: Department of Biology, University of Texas at San Antonio, San Antonio, TX 78249.

Molecular and Cellular Biology, February 2008, p. 1361-1372, Vol. 28, No. 4
0270-7306/08/$08.00+0     doi:10.1128/MCB.01291-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Koch, M. R., Pillus, L. (2009). From the Cover: The glucanosyltransferase Gas1 functions in transcriptional silencing. Proc. Natl. Acad. Sci. USA 106: 11224-11229 [Abstract] [Full Text]  
  • Kroetz, M. B., Su, D., Hochstrasser, M. (2009). Essential Role of Nuclear Localization for Yeast Ulp2 SUMO Protease Function. Mol. Biol. Cell 20: 2196-2206 [Abstract] [Full Text]  


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