CPS1(-POMBE GENE HOMOLOG OF SACCHAROMYCES-CEREVISIAE FKS GENES WHOSE MUTATION CONFERS HYPERSENSITIVITY TO CYCLOSPORINE-A AND PAPULACANDIN-B(), A SCHIZOSACCHAROMYCES)

The Schizosaccharomyces pombe cps1-12 (for chlorpropham supersensitive ) mutant strain was originally isolated as hypersensitive to the spind le poison isopropyl N-3-chlorophenyl carbamate (chlorpropham) (J. Ishi guro and Y. Uhara, Jpn. J. Genet. 67:97-109, 1992). We have found that the cps1-12 mutation also confers (i) hypersensitivity to the immunos uppressant cyclosporin A (CsA), (ii) hypersensitivity to the drug papu lacandin B, which specifically inhibits 1,3-beta-D-glucan synthesis bo th in vivo and in vitro, and (iii) thermosensitive growth at 37 degree s C. Under any of these restrictive treatments, cells swell up and fin ally lyse. With an osmotic stabilizer, cells do not lyse, but at 37 de grees C they become multiseptated and multibranched. The cps1-12 mutan t, growth at a restrictive temperature, showed an increase in sensitiv ity to lysis by enzymatic cell wall degradation, in in vitro 1,3-beta- D-glucan synthase activity (173% in the absence of GTP in the reaction ), and in cell wall biosynthesis (130% of the,wild-type amount). Addit ion of Ca2+ suppresses hypersensitivity to papulacandin B and septatio n and branching phenotypes. All of these data suggest a relationship b etween the cps1(+) gene and cell nail synthesis. A DNA fragment contai ning the cps1(+) gene was cloned, and sequence analysis indicated that it encodes a predicted membrane protein of 1,729 amino acids,vith 15 to 16 transmembrane domains. S. pombe cps1p has overall 55% sequence i dentity with Fks1p or Fks2p, proposed to be catalytic or associated su bunits of Saccharomyces cerevisiae 1,3-beta-D-glucan synthase. Thus, t he cps1(+) product might be a catalytic or an associated copurifying s ubunit of the fission yeast 1,3-beta-D-glucan synthase that plays an e ssential role in cell wall synthesis.