CHARACTERIZATION OF A MITOGEN-ACTIVATED PROTEIN-KINASE FROM PNEUMOCYSTIS-CARINII

The pathogenic fungus Pneumocystis carinii causes severe pneumonia in patients with impaired immunity, particularly patients with acquired i mmunodeficiency syndrome. The life cycle of P. carinii is poorly under stood, and the inability to continuously culture P. carinii is a major limitation in understanding its cell biology. In fungi homologous to P. carinii, pheromone mating factors signal through a mitogen-activate d protein kinase (MAPK) signal transduction cascade, resulting in mito tic cell cycle arrest and entry into a pathway of conjugation, cellula r differentiation, and proliferation. Using degenerate PCR and library screening, we have identified a MAPK cDNA in P. carinii that is highl y homologous to fungal MAPKs involved in the pheromone mating signal t ransduction cascade, and we demonstrate MAPK activity in P. carinii ly sates with a specific antiserum derived from the translated P. carinii MAPK cDNA sequence.