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.