THE YEAST SIN3 GENE-PRODUCT NEGATIVELY REGULATES THE ACTIVITY OF THE HUMAN PROGESTERONE-RECEPTOR AND POSITIVELY REGULATES THE ACTIVITIES OFGAL4 AND THE HAP1 ACTIVATOR

The activation of gene transcription in eukaryotic organisms is regula ted by sequence-specific DNA-binding proteins as well as by non-DNA-bi nding proteins. In this report we describe the modulatory functions of a non-DNA-binding protein, SIN3 (also known as SDI1, UME4, RPD1, and GAM2) on the transactivation properties of the human progesterone rece ptor (hPR), GAL4, and the HAP1 activator in yeast. Our data suggest th at SIN3 is a dual function protein. It negatively regulates the transc riptional activities of hPR-A and hPR-B by affecting the N-terminal ac tivation domain (AF1). SIN3 positively regulates the transcriptional a ctivities of GAL4 and the HAP1 activator. However, it has no effect on the transcriptional activities of the human glucocorticoid receptor ( hGR) and GCN4. The SIN3 protein contains four copies of a paired amphi pathic helix (PAH) motif. Deletion analysis of the SIN3 PAH motifs sho ws that the PAH3 motif is essential for SIN3-mediated regulation of hP R, GAL4, and the HAP1 activator. In constrast, the PAH1, PAH2, and PAH 4 motifs are not required for SIN3-mediated regulation of these activa tors. Additionally, we examined the mechanism(s) by which the SIN3 pro tein modulate the activities of various activators. We are unable to d emonstrate the direct interaction of SIN3 protein with these activator s using the yeast two-hybrid system or co-immunoprecipitation. These d ata suggest that SIN3 regulates the transactivation functions of hPR, GAL4, and the HAP1 activator by an indirect mechanism.