THE GLOBAL TRANSCRIPTIONAL REGULATORS, SSN6 AND TUP1, PLAY DISTINCT ROLES IN THE ESTABLISHMENT OF A REPRESSIVE CHROMATIN STRUCTURE

Repression of a-cell specific gene expression in yeast alpha cells req uires MAT alpha 2 and MCM1, as well as two global repressors, SSN6 and TUP1. Previous studies demonstrated that nucleosomes positioned adjac ent to the alpha 2/MCM1 operator in alpha cells directly contribute to repression. To investigate the possibility that SSN6 and TUP1 provide a link between MAT alpha 2/MCM1 and neighboring histones, nucleosome locations were examined in ssn6 and tup1 alpha cells. In both cases, n ucleosome positions downstream of the operator were disrupted, and the severity of the disruption correlated with the degree of derepression . Nevertheless, the observed changes in chromatin structure were not d ependent on transcription. Our data strongly indicate that SSN6 and TU P1 directly organize repressive regions of chromatin.