EFFECT OF PHENYLARSINE OXIDE ON THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE CELL-CYCLE

Phosphotyrosyl turnover is an essential regulatory mechanism for many biological processes, and the balance between tyrosine kinases and pho sphatases plays a major role in the control of cell proliferation. Phe nylarsine oxide (PAO), a potent inhibitor of tyrosine phosphatases (PT Pase), was used to investigate the involvement of PTPase in the growth and control of the cell cycle of the fission yeast Schizosaccharomyce s pombe. Cell proliferation was arrested by treatment with PAO, which was found to inhibit cdc25 PTPase in vitro but appeared not to act in vivo on this mitosis inducer. The PAO-treated cells displayed a mono- or binucleated phenotype and a DNA content that was either 2C or 4C, i ndicating a cell cycle arrest with a failure to complete cytokinesis. Entry into the cell division cycle from the G0 quiescent stage was als o delayed by treatment with PAO. These results suggest that a number o f key events in the mitotic cell cycle are regulated by as yet unident ified PTPases.