A MULTICOPY SUPPRESSOR OF A CELL-CYCLE DEFECT IN SCHIZOSACCHAROMYCES-POMBE ENCODES A HEAT SHOCK-INDUCIBLE 40 KDA CYCLOPHILIN-LIKE PROTEIN

Cyclophilins are peptidyl-prolyl cis-trans isomerases (PPIases) which have been implicated in intracellular protein folding, transport and a ssembly. Cyclophilins are also known as the intracellular receptors fo r the immunosuppressive drug cyclosporin A (CsA), The most common type of cyclophilins are the 18 kDa cytosolic proteins containing only the highly conserved core domain for PPIase and CsA binding activities, T he wis2(+) gene of the fission yeast Schizosaccharomyces pombe was iso lated as a multicopy suppressor of wee1-50 cdc25-22 win1-1, a triple m utant strain which exhibits a cell cycle defect phenotype. Sequence an alysis of wis2(+) reveals that it encodes a 40 kDa cyclophilin-like pr otein, homologous to the mammalian cyclophilin 40. The 18 kDa cyclophi lin domain (CyP-18) of wis2 is followed by a C-terminal region of 188 amino acids, The C-terminal region of wis2 is essential for suppressio n of the triple mutant defect, Furthermore, this region of the protein is able to confer suppression activity on the 18 kDa S.pombe cyclophi lin, cyp1, since a hybrid protein consisting of an 18 kDa S.pombe cycl ophilin (cyp1) fused to the C-terminus of wis2 shows suppression activ ity, We also demonstrate that the level of wis2(+) mRNA increases 10- to 20-fold upon heat shock of S.pombe cells, suggesting a role for wis 2(+) in the heat-shock response.