We have previously described the genetic analysis of eleven complementation groups ( sep6- sep16) defined by Schizosaccharomyces pombe mutants that are defective in cell separation and sexual differentiation. Here we report on the cloning and characterisation of two members of this set, sep10 and sep11. Sequencing of the full-length sep10 revealed a continuous ORF that encodes a conserved protein with possible functions in general transcriptional regulation. The coding region of sep11 is interrupted by introns and the putative s ep11 protein shows no sequence similarity with known proteins of other species. Disruption of each gene causes temperature sensitivity. Simultaneous disruption of both genes is lethal, demonstrating that sep10 and sep11 perform related, overlapping functions. Overexpression of aff1/ste11, a pivotal regulator of sexual development, suppresses the sterility of sep10 (-) cells, which suggests that sep10 is needed for the activity of aff1/ste11.