This family includes Saccharomyces cerevisiae mating type protein alpha 1. Mat alpha 1 is a transcription activator which activates mating-type alpha-specific genes. MAT alpha 1 and MCM 1 bind cooperatively to PQ elements upstream of alpha-specific genes. Alpha 1 interacts in vivo with STE12, linking expression of alpha-specific genes to the alpha-pheromone (pfam04648) response pathway. In silico modelling of the MAT_Alpha1 domain indicates that its best scoring templates were structures of HMG-box proteins, and DOI: 10.4236/ojbiphy.2013.31001. Phylogenetic analysis suggests that the MAT_Alpha1 domain diverged from the MATA_HMG-box subfamily. The name of MATalpha_HMG-box was proposed for the MAT_alpha1 domain.