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 α cells requires MATα2 and MCM1, as well as two global repressors, SSN6 and TUP1. Previous studies demonstrated that nucleosomes positioned adjacent to the α2/MCM1 operator in α cells directly contribute to repression. To investigate the possibility that SSN6 and TUP1 provide a link between MATα2/MCM1 and neighboring histones, nucleosome locations were examined in ssn6 and tup1 α cells. In both cases, nucleosome 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 dependent on transcription. Our data strongly indicate that SSN6 and TUP1 directly organize repressive regions of chromatin.