The Fission Yeast GATA Factor, Gaf1, Modulates Sexual Development via Direct Down-Regulation of ste11(+) Expression in Response to Nitrogen Starvation

Gaf1 is the first GATA family zinc-finger transcription factor identified in Schizosaccharomyces pombe. Here, we report that Gaf1 functions as a negatively acting transcription factor of ste11(+), delaying the entrance of cells exposed to transient nitrogen starvation into the meiotic cycle. gaf1Δ strains exhibited accelerated G(1)-arrest upon nitrogen starvation. Moreover, gaf1Δ mutation caused increased mating and sporulation frequency under both nitrogen-starved and unstarved conditions, while overexpression of gaf1(+) led to a significant impairment of sporulation. By microarray analysis, we found that approximately 63% (116 genes) of the 183 genes up-regulated in unstarved gaf1Δ cells were nitrogen starvation-responsive genes, and furthermore that 25 genes among the genes up-regulated by gaf1Δ mutation are Ste11 targets (e.g., gpa1 (+), ste4 (+), spk1 (+), ste11 (+), and mei2 (+)). The phenotype caused by gaf1Δ mutation was masked by ste11Δ mutation, indicating that ste11(+) is epistatic to gaf1(+) with respect to sporulation efficiency, and accordingly that gaf1(+) functions upstream of ste11(+) in the signaling pathway governing sexual development. gaf1Δ strains showed accelerated ste11(+) expression under nitrogen starvation and increased ste11(+) expression even under normal conditions. Electrophoretic mobility shift assay analysis demonstrated that Gaf1 specifically binds to the canonical GATA motif (5′-HGATAR-3′) spanning from −371 to −366 in ste11(+) promoter. Consequently, Gaf1 provides the prime example for negative regulation of ste11(+) transcription through direct binding to a cis-acting motif of its promoter.