The SKS1 protein kinase is a multicopy suppressor of the snf3 mutation of Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae strains carrying snf3 are defective in high affinity glucose transport, and thus are unable to grow fermentatively on media with low concentrations of glucose. A multicopy suppressor of the snf3 growth defect, SKS1 (suppressor kinase of snf3), was found to encode a putative ser/thr protein kinase homologous to Ran1p, a kinase that regulates the switch between meiosis and vegetative growth in Schizosaccharomyces pombe. Overexpression of the SKS1 open reading frame is sufficient for suppression of the growth defects of snf3 mutants. Disruption of the open reading frame eliminates this suppression; as does the mutation of the consensus ATP binding site of Sks1p. A DDSE (DNA dependent snf3 suppressor element) was found to be present in the SKS1 promoter region. The suppression by this DDSE occurs in the absence of SKS1 coding region, that is, the DDSE can suppress a snf3 sks1 double null mutant which fails to grow fermentatively on low glucose as a snf3 mutant does. Both SKS1 and its DDSE can additionally suppress the growth defects of grr1 mutants, which are also impaired in high affinity glucose transport. The snf3 genomic suppressors, rgt1, RGT2 and ssn6, are also capable of suppressing snf3 associated growth defects in a strain lacking sks1.