AN RNA-BINDING PROTEIN NEGATIVELY CONTROLLING DIFFERENTIATION IN FISSION YEAST

The fission yeast Schizosaccharomyces pombe starts sexual development when starved for nutrients and simultaneously activated by mating pher omones. We have identified a new gene regulating the onset of this pro cess. This gene, called nrd1(+), encodes a typical RNA binding protein that preferentially binds poly(U). Deletion of nrd1(+) causes cells t o initiate sexual development without nutrient starvation. We have fou nd that the biological role of nrd1(+) is to block the onset of sexual development by repressing the Ste11-regulated genes essential for con jugation and meiosis until cells reach a critical level of starvation.