THE CARBOXY-TERMINAL TAIL OF THE HOMEO DOMAIN PROTEIN-ALPHA-2 IS REQUIRED FOR FUNCTION WITH A 2ND HOMEO DOMAIN PROTEIN

The homeo domain protein alpha2 from Saccharomyces cerevisiae has two roles in the a/alpha cell: With MCM1, alpha2 turns off transcription of a-specific genes; with a1 (a second homeo domain protein), alpha2 represses transcription of haploid-specific genes. From the carboxy-terminal side of the alpha2 homeo domain extends an unstructured 22-amino-acid residue tail. In this paper we show that the carboxy-terminal tail of alpha2 is required for formation of a stable a1/alpha2-operator complex and is thus required for a1/alpha2-mediated repression of transcription. In contrast, the tail is dispensable for alpha2/MCM1-mediated repression. These results indicate that a short, unstructured tail mediates the interaction between two homeo domain proteins.