cps1 +, a Schizosaccharomyces pombe gene homolog of Saccharomyces cerevisiae FKS genes whose mutation confers hypersensitivity to cyclosporin A and papulacandin B

Abstract

The Schizosaccharomyces pombe cps1-12 (for chlorpropham supersensitive) mutant strain was originally isolated as hypersensitive to the spindle poison isopropyl N-3-chlorophenyl carbamate (chlorpropham) (J. Ishiguro and Y. Uhara, Jpn. J. Genet. 67:97-109, 1992). We have found that the cps1-12 mutation also confers (i) hypersensitivity to the immunosuppressant cyclosporin A (CsA), (ii) hypersensitivity to the drag papulacandin B, which specifically inhibits 1,3-β-D-glucan synthesis both in vivo and in vitro, and (iii) thermosensitive growth at 37°C. Under any of these restrictive treatments, cells swell up and finally lyse. With an osmotic stabilizer, cells do not lyse, but at 37°C they become multiseptated and multibranched. The cps1-12 mutant, grown at n restrictive temperature, showed an increase in sensitivity to lysis by enzymatic cell wall degradation, in in vitro 1,3-β- D-glucan synthase activity (173% in the absence of GTP in the reaction), and in cell wall biosynthesis (130% of the wild-type amount). Addition of Ca 2+ suppresses hypersensitivity to papulacandin B and septation and branching phenotypes. All of these data suggest a relationship between the eps1 + gene and cell wall synthesis. A DNA fragment containing the cps1 + gene was cloned, and sequence analysis indicated that it encodes a predicted membrane protein of 1,729 amino acids with 15 to 16 transmembrane domains. S. pombe cps1p has overall 55% sequence identity with Fks1p or Fks2p, proposed to be catalytic or associated subunits of Saccharomyces cerevisiae 1,3-β-D-glucan synthase. Thus, the cps1 + product might be a catalytic or an associated copurifying subunit of the fission yeast 1,3-β-D-glucan synthase that plays an essential role in cell wall synthesis.