Indirect suppression of the wee1 mutant phenotype in Schizosaccharomyces pombe.

For S. pombe cells mutations in the wee1 regulatory gene have been shown previously to allow cells to be smaller than normal at cell division, to endow the cell with a significantly long G1 cell cycle interval, and to alter the timing in the cell cycle of certain mutationally-defined cell cycle steps in G2. We show here that situations which lengthen S phase in proliferating wee1 mutant cells 'suppress' to varying degrees these wee1-mediated cell cycle alterations. Conditions chosen to protract S phase were use of cdc22.M45 mutant cells at semipermissive temperatures, and the presence of sub-arresting concentrations of the S phase inhibitors hydroxyurea or deoxyadenosine. Proliferation in the presence of each of these inhibitors was shown directly to result in protracted S phase. Residual cell division measurements were used to measure the cell cycle timing of G1 and G2 cell-cycle steps. The indirect suppression of the wee1 phenotype shown here can be understood in terms of the proposed role of the wee1+ gene product in coordinating cell division with cellular growth.