Protein kinase C in Saccharomyces cerevisiae: comparison with the mammalian enzyme.

Protein kinase C (PKC) was detected in the yeast Saccharomyces cerevisiae with bovine myelin basic protein as the phosphate acceptor. The enzyme was purified at least 500-fold by a four-step column chromatographic procedure (phenyl-Sepharose CL-4B, Mono Q, Heparin-5PW, and hydroxyapatite). The molecular mass was approximately 90 kDa, as estimated by gel-filtration analysis. Yeast PKC was activated by the simultaneous addition of Ca2+, diacylglycerol, and phosphatidylserine. Free arachidonic acid alone could activate the enzyme to some extent. However, yeast PKC did not respond significantly to tumor-promoting phorbol esters. GTP did not serve as phosphate donor. The yeast enzyme showed substrate specificity distinctly different from that of mammalian PKCs. H1 histone and protamine were poor substrates. With myelin basic protein as a model substrate, yeast PKC phosphorylated threonyl residues preferentially, whereas rat brain PKCs phosphorylated seryl residues preferentially. Further studies should elucidate the role of yeast PKC in cellular regulation and cell cycle control.