Analysis of Spt7 Function in the Saccharomyces cerevisiae SAGA Coactivator Complex

Abstract

The Saccharomyces cerevisiae SAGA complex is required for the normal transcription of a large number of genes. Complex integrity depends on three core subunits, Spt7, Spt20, and Ada1. We have investigated the role of Spt7 in the assembly and function of SAGA. Our results show that Spt7 is important in controlling the levels of the other core subunits and therefore of SAGA. In addition, partial SAGA complexes containing Spt7 can be assembled in the absence of both Spt20 and Ada1. Through biochemical and genetic analyses of a series of spt7 deletion mutants, we have identified a region of Spt7 required for interaction with the SAGA component Spt8. An adjacent Spt7 domain was found to be required for a processed form of Spt7 that is present in a previously identified altered form of SAGA called SLIK, SAGA_alt, or SALSA. Analysis of an spt7 mutant with greatly reduced levels of SLIK/SAGA_alt/SALSA suggests a subtle role for this complex in transcription that may be redundant with a subset of SAGA functions.

We thank Joe Martens and Erica Larschan for helpful comments on the manuscript and members of the Winston laboratory for stimulating discussions. We are grateful to Shelley Berger, David Sterner, and Patrick Grant for sharing unpublished data. We thank Jerry Workman and Shigehiro Osada for their hospitality and invaluable aid with SAGA purification techniques. We thank Shelley Berger, Michael Green, Lenny Guarente, Jerry Workman, and Patrick Grant for providing antibodies to SAGA subunits. We also thank Bertrand Séraphin for plasmids.

P.-Y.W. was supported by a Predoctoral Fellowship from the Howard Hughes Medical Institute. This work was supported by National Institutes of Health grant GM45720 to F.W.