THE YEAST CCR4 PROTEIN IS NEITHER REGULATED BY NOR ASSOCIATED WITH THE SPT6 AND SPT10 PROTEINS AND FORMS A FUNCTIONALLY DISTINCT COMPLEX FROM THAT OF THE SNF SWI TRANSCRIPTION FACTORS/

The CCR4 protein is specifically required for the increased transcript ion at the ADH2 locus resulting from mutations in the SPT10 (CRE1) and SPT6 (CRE2) genes and is also required for the expression of ADH2 and other genes under non-fermentative growth conditions. The mechanism b y which mutations in CCR4 suppress defects in SPT10 and SPT6 was exami ned. The SPT10 and SPT6 genes were shown not to control CCR4 mRNA or p rotein expression nor did SPT10 and SPT6 proteins co-immuneprecipitate with CCR4. CCR4 association with two other proteins, 195 and 185 kDa in size, was unaffected by either sp10 or spt6 mutations. Also, the ab ility of CCR4 to activate transcription when fused to the LexA DNA bin ding domain was not specifically enhanced by defects in either SPT10 o r SPT6. These results suggest that SPT10 and SPT6, in negatively regul ating transcription at ADH2, act through a factor that requires CCR4 f unction, but do not regulate CCR4 expression, control its activity, ph ysically interact with it, or affect its binding to other factors. The relationship of CCR4 to the group of general transcription factors, S NF2, SNF5, SNF6 and SW11 and SW13, which comprise a multisubunit compl ex required for ADH2 and other genes' expression, was also examined. C CR4 protein expression was not controlled by these factors nor did the y co-immuneprecipitate or associate with CCR4. In addition, a ccr4 mut ation had little effect on an ADH2 promoter alteration in contrast to the large effects displayed by mutations in SNF2 and SNF5. These data suggest that CCR4 acts by a separate mechanism from that used by the S NF/SWI general transcription factors in affecting gene expression.