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 o f a-specific genes; with a1 (a second homeo domain protein), alpha2 re presses transcription of haploid-specific genes. From the carboxy-term inal side of the alpha2 homeo domain extends an unstructured 22-amino- acid residue tail. In this paper we show that the carboxy-terminal tai l of alpha2 is required for formation of a stable a1/alpha2-operator c omplex and is thus required for a1/alpha2-mediated repression of trans cription. In contrast, the tail is dispensable for alpha2/MCM1-mediate d repression. These results indicate that a short, unstructured tail m ediates the interaction between two homeo domain proteins.