FIG. 1.

RE regulation and donor preference during mating-type switching in Saccharomyces cerevisiae. (A) Donor preference in MATα cells. A schematic representation of the mating-type locus (MAT), the two silent donor loci (HML and HMR), and the RE is shown. In MATα cells, the Matα2-Mcm1 complex recruits the general repressor Tup1 to RE, inactivating RE by formation of highly organized nucleosomes, resulting in the preferred use of HMR. (B) Donor preference in MATa cells. Mcm1 binds to the RE and removes the positioned nucleosomes, allowing binding of trans-acting factors, including Fkh1 and SBF, leading to activation of RE and consequently to the favored usage of HML.