Mating type proteins are sequence specific DNA-binding proteins that act as master switches in yeast differentiation by controlling gene expression in a cell type-specific fashion. Transcriptional corepressor that binds cooperatively with MCM1 to a 31-basepair DNA sequence termed the a-specific gene (asg) operator, to repress the transcription of a-cell-specific genes. Additionally, in a/alpha diploid cells, binds cooperatively with the A1 protein to a 21-basepair DNA sequence termed the haploid-specific gene (hsg) operator, to repress transcription of haploid-specific genes and of MATALPHA1. Binds DNA with a high specificity as a heterotetramer consisting of an ALPHA2 dimer and an MCM1 dimer. Also binds DNA with a high specificity as a heterodimer of A1 and ALPHA2 in a/alpha diploid cells. Interacts with the general transcription repressor complex SSN6/TUP1. Only present in alpha-cells and in a/alpha diploid cells. The N-terminal domain is required for the interaction with the WD repeats of TUP1 and for dimerization. The homeobox domain binds to DNA and interacts with the TPR repeats of SSN6. The unstructured, flexible linker domain contains eight residues (Leu-114 to Gln-121), which, in the presence of MCM1, adopt a beta-fold and mediate the cooperative interaction to MCM1. The C-terminal tail domain is disordered in the monomer, even when bound to DNA. In the ternary complex with A1 and DNA, 16 residues (Ile-190 to Leu-205) of the C-terminal tail undergo a conformational change, becoming ordered and contacting the A1 homeodomain. There are three genetic loci for mating type genes in S.cerevisiae. MAT is the expression locus that determines the mating type of the cell, whereas HML (containing HMLALPHA1 and HMLALPHA2) and HMR (containing HMRA1 and HMRA2) represent silenced repositories of mating type information. The mating type is determined by the MAT locus, which contains either a copy of HML or of HMR. Diploid cells are usually heterozygous for the MAT locus. Belongs to the TALE/M-ATYP homeobox family.