MULTICOPY FZF1 (SUL1) SUPPRESSES THE SULFITE SENSITIVITY BUT NOT THE GLUCOSE DEREPRESSION OR ABERRANT CELL MORPHOLOGY OF A GRR1 MUTANT OF SACCHAROMYCES-CEREVISIAE

An ssu2 mutation in Sacccharomyces cerevisiae, previously shown to cau se sulfite sensitivity, was found to be allelic to GRR1, a gene previo usly implicated in glucose repression. The suppressor rgt1, which supp resses the growth defects of grr1 strains on glucose, did not fully su ppress the sensitivity on glucose or nonglucose carbon sources, indica ting that it is not strictly linked to a defect in glucose metabolism. Because the Cln1 protein was previously shown to be elevated in grr1 mutants, the effect of CLN1 overexpression on sulfite sensitivity was investigated. Overexpression in GRR1 cells resulted in sulfite sensiti vity, suggesting a connection between CLN1 and sulfite metabolism. Mul ticopy FZF1, a putative transcription factor, was found to suppress th e sulfite sensitive phenotype of grr1 strains, but not the glucose der epression or aberrant cell morphology. Multicopy FZF1 was also found t o suppress the sensitivity of a number of other unrelated sulfite-sens itive mutants, but not that of ssu1 or met20, implying that FZF1 may a ct through Ssu1p and Met20p. Disruption of FZF1 resulted in sulfite se nsitivity when the construct was introduced in single copy at the FZF1 locus in a GRR1 strain, providing evidence that FZF1 is involved in s ulfite metabolism.