IDENTIFICATION OF AN ASYMMETRICALLY LOCALIZED DETERMINANT, ASH1P, REQUIRED FOR LINEAGE-SPECIFIC TRANSCRIPTION OF THE YEAST HO GENE

S. cerevisiae cells exhibit asymmetric determination of cell fate. Cel l division yields a mother cell, which is competent to transcribe the HO gene and switch mating type, and a daughter cell, which is not. We have isolated a mutant in which daughters transcribe HO and switch mat ing type. This mutation defines the ASH1 gene (asymmetric synthesis of HO). Deletion and overexpression of ASH1 cause reciprocal cell fate t ransformations: in ash1 Delta strains, daughters switch mating type as efficiently as mothers. Conversely, overexpression of ASH1 inhibits s witching in mother cells. Ash1p has a zinc finger motif related to tho se of GATA transcriptional regulators. Ash1p is localized to the daugh ter nucleus in cells that have undergone nuclear division. Thus, Ash1p is a cell fate determinant that is asymmetrically localized to the da ughter nucleus where it inhibits HO transcription.