Pneumocystis carinii is an opportunistic fungus causing severe pneumonia in immune-compromised hosts. Recent evidence suggests that Pneumocystis exists as separate sex types, though definitive evidence is currently lacking. These studies were undertaken to determine whether Pneumocystis maintains functional meiotic control molecules, which are required for sexual life stages in eukaryotes. Using the Pneumocystis carinii Genome Project database, two partial sequences for meiotic control molecules were detected, namely, PCRan1, a presumptive meiotic control kinase, and PCMei2, a homologue to a primary activator of meiosis in Schizosaccharomyces pombe. Rapid amplification of cDNA ends was employed to obtain the full open reading frames and to further investigate the functions of these proteins. These presumptive meiotic control molecules were most homologous to molecules present in S. pombe (52% identical and 67% homologous for PCRan1 and 75% identical and 88% homologous for PCMei2 by BLAST analysis). Heterologous expression of these Pneumocystis meiotic genes in corresponding temperature-sensitive and knockout strains of S. pombe, respectively, further verified the functions of the PCRan1 and PCMei2 proteins. These proteins were further shown to control downstream components of the meiotic pathway in S. pombe. Lastly, in vitro kinase assays were used to determine that PCRan1p phosphorylates PCMei2p. These experiments represent the first characterization of any proteins in P. carinii involved in meiosis and indicate the presence of a conserved meiotic pathway in Pneumocystis. Elucidation of this pathway will be essential in gaining a greater understanding of this important opportunistic fungal pathogen.