GENES REQUIRED FOR DEREPRESSION OF AN EXTRACELLULAR GLUCOAMYLASE GENE, STA2, IN THE YEAST SACCHAROMYCES

A diastatic strain of Saccharomyces cerevisiae producing the STA2-enco ded extracellular glucoamylase (GA) in a pronounced glucose-repressibl e fashion was used as a parent for generating mutants with reduced GA activity under normal conditions of derepression. In addition to mutat ions in STA2, five other recessive mutations were identified which fel l into four complementation groups designated haf1 through haf4. RNA b lot analysis suggested that the haf mutations confer defects in STA2 t ranscription. The haf mutants were pleiotropically defective in utiliz ation of alternative carbon sources and resembled the snf (sucrose non -fermenting) mutants identified previously as unable to derepress the expression of the SUC2 gene encoding invertase. We present evidence st rongly suggesting that haf1 = snf2, haf3 = snf1 and haf4 = snf5. By ph enotypic criteria, the postulated HAF2 gene (which is none of the SNF genes tested) appears to be similar to SNF2, SNF5 and SNF6, and is pos sibly a non-redundant extension of this group of functionally related SNF genes.