IDENTIFICATION AND ANALYSIS OF MOT3, A ZINC-FINGER PROTEIN THAT BINDSTO THE RETROTRANSPOSON TY LONG TERMINAL REPEAT (DELTA) IN SACCHAROMYCES-CEREVISIAE

Spt3 and Mot1 are two transcription factors of Saccharomyces cerevisia e that are thought to act in a related fashion to control the function of TATA-binding protein (TBP), Current models suggest that while Spt3 and Mot1 do not directly interact, they do function in a related fash ion to stabilize the TBP-TATA interaction at particular promoters. Con sistent with this model, certain combinations of spt3 and mot1 mutatio ns are inviable, To identify additional proteins related to Spt3 and M ot1 functions, we screened for high-copy-number suppressors of the mot 1 spt3 inviability. This screen identified a previously unstudied gene , MOT3, that encodes a zinc finger protein. We show that Mot3 binds in vitro to three sites within the retrotransposon Ty long terminal repe at (delta) sequence. One of these sites is immediately 5' of the delta TATA region, Although a mot3 null mutation causes no strong phenotype s, it does cause some mild phenotypes, including a very modest increas e in Ty mRNA levels, partial suppression of transcriptional defects ca used by a mot1 mutation, and partial suppression of an spt3 mutation. These results, in conjunction with those of an independent study of Mo t3 (A. Grishin, M, Rothenberg, M, A. Downs, and K. J. Blumer, Genetics , in press), suggest that this protein plays a varied role in gene exp ression that may be largely redundant with other factors.