The role of nucleosome positioning in repression by the yeast alpha 2/Mcm1p repressor.

In Saccharomyces cerevisiae, alpha 2/Mcm1p represses a-cell specific genes. Previous studies indicated that repression by alpha 2/Mcm1p is associated with organization of positioned nucleosomes in promoters of a-cell specific genes such as STE6 and BAR1. Here, we examined the role of nucleosome positioning in repression of STE6-lacZ by alpha 2/Mcm1p. We showed that insertion of an A34 sequence, which is shown to disrupt an array of positioned nucleosomes, affects STE6-lacZ expression. Furthermore, artificial recruitment of TBP is facilitated by the insertion of A34 to derepress STE6-lacZ expression. These findings support the model that nucleosome positioning plays a regulatory role in repression by alpha 2/Mcm1p.