Novel Factor Highly Conserved among Eukaryotes Controls Sexual Development in Fission Yeast

In the fission yeast Schizosaccharomyces pombe, the onset of sexual development is controlled mainly by two external signals, nutrient starvation and mating pheromone availability. We have isolated a novel gene named rcd1(+) as a key factor required for nitrogen starvation-induced sexual development. rcd1(+) encodes a 283-amino-acid protein with no particular motifs. However, genes highly homologous to rcd1(+) (encoding amino acids with >70% identity) are present at least in budding yeasts, plants, nematodes, and humans. Cells with rcd1(+) deleted are sterile if sexual development is induced by nitrogen starvation but fertile if it is induced by glucose starvation. This results largely from a defect in nitrogen starvation-invoked induction of ste11(+), a key transcriptional factor gene required for the onset of sexual development. The striking conservation of the gene throughout eukaryotes may suggest the presence of an evolutionarily conserved differentiation controlling system.