Sucl+ was originally identified as a DNA sequence that, at high copy number, rescued Schizosaccharomyces pombe strains carrying certain temperature-sensitive alleles of the cdc2 cell cycle control gene. We determined the nucleotide sequence of a 1,083-base-pair Sucl+ DNA fragment and S1 mapped its 866-nucleotide RNA transcript. The protein-coding sequence of the gene is interrupted by two intervening sequences of 115 and 51 base pairs. The predicted translational product of the gene is a protein of 13 kilodaltons. A chromosomal gene disruption of Sucl+ was constructed in a diploid S. pombe strain. Germinating spores carrying a null allele of the gene were capable of very limited cell division, following which many cells became highly elongated. The Sucl+ gene was also strongly overexpressed under the control of a heterologous S. pombe promoter. Overexpression of Sucl+ is not lethal but causes a division delay such that cells are approximately twice the normal length at division. These data suggest that Sucl+ encodes a protein which plays a direct role in the cell division cycle of S. pombe.