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. Positive regulator of MFM genes. The HMG box recognizes the DNA sequence 5'-AACAAAG-3'. Required for conjugation and efficient meiosis (By similarity). There are three genetic loci for mating type genes in fission yeast, mat1, mat2-P and mat3-M. Cell type is determined by the alternate allele present in mat1, either P (plus) in a h+ or M (minus) in a h- cell. Mat2-P and mat3-M serve as donor of information that is transposed to mat1 during a switch of mating type (By similarity).