Ubp10/Dot4p Regulates the Persistence of Ubiquitinated Histone H2B: Distinct Roles in Telomeric Silencing and General Chromatin

Abstract

We previously discovered that the ubiquitin protease Ubp10/Dot4p is important for telomeric silencing through its interaction with Sir4p. However, the mechanism of Ubp10p action was unknown. We now provide evidence that Ubp10p removes ubiquitin from histone H2B; cells with UBP10 deleted have increased steady-state levels of H2B ubiquitination. As a consequence, ubp10Δ cells also have increased steady-state levels of histone H3 Lys4 and Lys79 methylation. Consistent with its role in silencing, Ubp10p is preferentially localized to silent chromatin where its ubiquitin protease activity maintains low levels of H3 Lys4 and Lys79 methylation to allow optimal Sir protein binding to telomeres and global telomeric silencing. The ubiquitin protease Ubp8p has also been shown to remove ubiquitin from H2B, and ubp8Δ cells have increased steady-state levels of H2B ubiquitination similar to those in ubp10Δ cells. Unlike ubp10Δ cells, however, ubp8Δ cells do not have increased steady-state levels of H3 Lys4 and Lys79 methylation, nor is telomeric silencing affected. Despite their separate functions in silencing and SAGA-mediated transcription, respectively, deletion of both UBP10 and UBP8 results in a synergistic increase in the steady-state levels of H2B ubiquitination and in the number of genes with altered expression, indicating that Ubp10p and Ubp8p likely overlap in some of their target chromatin regions. We propose that Ubp10p and Ubp8p are the only ubiquitin proteases that normally remove monoubiquitin from histone H2B and, while there are regions of the genome to which each is specifically targeted, both combine to regulate the global balance of H2B ubiquitination.

SUPPLEMENTAL MATERIAL

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

ACKNOWLEDGMENTS

We thank M. A. Osley for the FLAG-tagged H2B plasmids and J. Delrow for statistical analysis of the transcript microarray data. We thank H. Eisen and the members of the Gottschling lab for insightful discussions and critical reading of the manuscript.

R.G.G. is a Bristol Myers Squibb fellow of the Life Sciences Research Foundation. This work was supported by National Institutes of Health grant GM43893 to D.E.G.