Molecular cloning and characterization of a fission yeast gene responsible for supersensitivity to the spindle poison, isopropyl N-3-chlorophenyl carbamate.

The cps3 gene of the fission yeast, Schizosaccharomyces pombe, was previously identified as a mutation conferring supersensitivity to the spindle poison, isopropyl N-3-chlorophenyl carbamate (CIPC). A 3.2 kb DNA fragment that complements the mutant phenotype was cloned from a S. pombe genomic library. The base sequence analysis showed that the fragment contains a maximum 1086 nucleotide open reading frame and that the putative product consists of 362 amino acids, having a molecular weight of 39.3 KDa. No significant homology of the potential product with known proteins could be found by database searches. A disruptant of the gene, produced by insertion of a ura4+ fragment was able to germinate, but not to undergo cell division, suggesting that the gene to be essential for the cell cycle progression. The disruption experiment suggests that the gene is an extragenic suppressor of cps3 mutation.

Isolation and characterization of mutants supersensitive to the spindle poison, isopropyl N-3-chlorophenyl carbamate (CIPC) in the fission yeast Schizosaccharomyces pombe.

Mutants supersensitive to the spindle poison, Isopropyl N-3-chlorophenyl carbamate (CIPC) of the fission yeast Schizosaccharomyces pombe were isolated and characterized genetically. Fourteen different recessive loci were assigned for the mutation (donated as cps1 to cps14) and two, cps1 and cps3, were mapped precisely on the chromosomes. Nine mutant strains were also supersensitive to phenothiazine derivatives, inhibitors of calcium-binding protein calmodulin. Four of nine strains were incapable of growing in the presence of 10 microM calcium ionophore A23187, at which the drug had no effect on cell growth in other strains. Fluorescence microscopy using the DAPI and Calcofluor staining methods showed two strains out of four to be defective in normal cell division; most stationary-phase cells of the cps6 mutant were seen to be bi- or tetra-nucleate, being partitioned with one or three septa, respectively. In the other mutant (cps8), enlarged cells were unequally partitioned with multisepta, and each compartment contained several daughter nuclei. The septa appeared aberrant in position within the cell, and situated diagonally but not vertically along the long cell axis.