QUANTITATION OF PROTEIN PHOSPHATASE-1 AND PROTEIN PHOSPHATASE-2A IN EXTRACTS OF THE BUDDING YEAST AND FISSION YEAST

Serine/threonine protein phosphatases are also involved in the control of cell division. The aim of the present study was to compare the act ivity of protein phosphatase 1 (PPI) and 2A (PP2A) in cell extracts of the budding and fission yeast, made at different phases of growth. Th e activities of PP1 and PP2A toward phosphorylase were similar in extr acts of S. cerevisiae. In S. pombe extracts, PP1 was responsible for m ore than 80% of the phosphorylase phosphatase activity. Ammonium sulfa te-ethanol treatment increased the specific activity of the phosphatas es and the percentage of PP2A in S. cerevisiae extracts. No increase i n the proportion of PP2A was observed upon the same treatment of S. po mbe extracts. The above results were confirmed by fractionation of PP1 and PP2A activities on a heparin-Sepharose column. The proportion of PP1 and PP2A activities did not change significantly during exponentia l cell growth but cells from stationary phase exhibited lower phosphat ase activities. These results may indicate a lower level of expression of the PP2A genes in S. pombe and/or differences in the structure of the holoenzymes or their regulators in the two genera.