The Schizosaccharomyces pombe pyp1+ gene, encoding a protein tyrosine phosphatase (pyp1), was isolated as a high copy number suppressor of a mutation that results in reduced cAMP-dependent protein kinase (PKA) activity. Overexpression of pyp1+ inhibits both transcription of the fbp1 gene, which is negatively regulated by a glucose-induced activation of PKA, and sexual development, which is negatively regulated by PKA through a nitrogen- and glucose-monitoring mechanism. Overexpression of a catalytically inactive form of pyp1 has little effect on either process. Previous studies suggest that overexpression of pyp1+ results in a mitotic delay by positively regulating wee1 activity. We show that pyp1 repression of fbp1 transcription is independent of wee1. The direct role of the pyp1 protein is to dephosphorylate and inactivate the sty1/spc1 mitogen-activated protein kinase (MAPK) that is activated by the wis1 MAPK kinase. As overexpression of pyp1+ has no further effect upon the mitotic delay observed in a wis1 deletion strain, the role of pyp1 appears to be restricted to negative regulation of the sty1/spc1 MAPK. This study indicates that pyp1 negatively regulates fbp1 transcription, sexual development and mitosis by inactivation of the sty1/spc1 MAPK, but that bifurcations downstream of the MAPK separate these processes as seen by the differential role for the wee1 gene.