H2B Ubiquitin Protease Ubp8 and Sgf11 Constitute a Discrete Functional Module within the Saccharomyces cerevisiae SAGA Complex

Abstract

The SAGA complex is a multisubunit protein complex involved in transcriptional regulation in Saccharomyces cerevisiae. SAGA combines proteins involved in interactions with DNA-bound activators and TATA-binding protein (TBP), as well as enzymes for histone acetylation (Gcn5) and histone deubiquitylation (Ubp8). We recently showed that H2B ubiquitylation and Ubp8-mediated deubiquitylation are both required for transcriptional activation. For this study, we investigated the interaction of Ubp8 with SAGA. Using mutagenesis, we identified a putative zinc (Zn) binding domain within Ubp8 as being critical for the association with SAGA. The Zn binding domain is required for H2B deubiquitylation and for growth on media requiring Ubp8's function in gene activation. Furthermore, we identified an 11-kDa subunit of SAGA, Sgf11, and showed that it is required for the Ubp8 association with SAGA and for H2B deubiquitylation. Different approaches indicated that the functions of Ubp8 and Sgf11 are related and separable from those of other components of SAGA. In particular, the profiles of Ubp8 and Sgf11 deletions were remarkably similar in microarray analyses and synthetic genetic interactions and were distinct from those of the Spt3 and Spt8 subunits of SAGA, which are involved in TBP regulation. These data indicate that Ubp8 and Sgf11 likely represent a new functional module within SAGA that is involved in gene regulation through H2B deubiquitylation.

ACKNOWLEDGMENTS

We gratefully acknowledge S. Kochbin for directing our attention to the similar Zn finger sequences in HDAC6 and Ubp8 and thank L. J. Duggan for the generation of the Ada2-TAP strain used for the immunoprecipitation of SAGA subunits.

This work was supported by research grants from the National Institutes of Health (GM 55360 to S.L.B) and the National Science Foundation (MCB-0078940 to S.L.B). An NIH training grant supported A.W. (T32 GM008216). A doctoral fellowship from the University of Pennsylvania—Biomedical Graduate Studies supported K.I. N.J.K. was supported by a doctoral fellowship from the Canadian Institutes of Health Research. This research was supported by grants to J.F.G. from the Canadian Institutes of Health Research, the Ontario Genomics Institute, and the National Cancer Institute of Canada with funds from the Canadian Cancer Society.