SKN1 and KRE6 define a pair of functional homologs encoding putative membrane proteins involved in beta-glucan synthesis.
KRE6 encodes a predicted type II membrane protein which, when disrupted, results in a slowly growing, killer toxin-resistant mutant possessing half the normal level of a structurally wild-type cell wall (1-->6)-beta-glucan (T. Roemer and H. Bussey, Proc. Natl. Acad. Sci. USA 88:11295-11299, 1991). The mutant phenotype and structure of the KRE6 gene product, Kre6p, suggest that it may be a beta-glucan synthase component, implying that (1-->6)-beta-glucan synthesis in Saccharomyces cerevisiae is functionally redundant. To examine this possibility, we screened a multicopy genomic library for suppression of both the slow-growth and killer resistance phenotypes of a kre6 mutant and identified SKN1, which encodes a protein sharing 66% overall identity to Kre6p. SKN1 suppresses kre6 null alleles in a dose-dependent manner, though disruption of the SKN1 locus has no effect on killer sensitivity, growth, or (1-->6)-beta-glucan levels. skn1 kre6 double disruptants, however, showed a dramatic reduction in both (1-->6)-beta-glucan levels and growth rate compared with either single disruptant. Moreover, the residual (1-->6)-beta-glucan polymer in skn1 kre6 double mutants is smaller in size and altered in structure. Since single disruptions of these genes lead to structurally wild-type (1-->6)-beta-glucan polymers, Kre6p and Skn1p appear to function independently, possibly in parallel, in (1-->6)-beta-glucan biosynthesis.
Roemer
T
T
Biology Department, McGill University, Montreal, Quebec, Canada.
Delaney
S
S
Bussey
H
H
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005936:Glucans / Q000096:biosynthesis*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010641:Phenotype; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic
D005656:Fungal Proteins; D005936:Glucans; C081933:KRE6 protein, S cerevisiae; D008565:Membrane Proteins; C081932:SKN1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins