Pyrimidine ribonucleoside monophosphokinase and the mode of RNA turnover in Bacillus subtilis

Abstract

A protein catalyzing the phosphorylation of CMP to CDP was purified and characterized. Kinase activity for UMP copurified during ammonium sulfate fractionation, DEAE-cellulose and hydroxylapatite chromatography, and gel filtration on Sephadex G-75, the ratios of activities for the two substrates remaining constant. The purified product, possessing both activities was homogeneous as judged by the single band following polyacrylamide gel electrophoresis. The protein showed no kinase activity against purine nucleoside monophosphates or the other pyrimidine nucleoside monophosphates: dCMP, dUMP, and dTMP. Thus unlike the enteric bacteria, Escherichia coli and Salmonella typhimurium which have distinct enzymes which phosphorylate UMP and CMP, Bacillus subtilis produces a single pyrimidine ribonucleoside monophosphokinase. The Km values of this enzyme from B.subtilis are 0.04 and 0.25 mM for CMP and UMP, respectively, and 0.04 and 0.4 mM for ATP at saturating concentrations of CMP and UMP, respectively. The properties of this enzyme and the differences between enteric bacteria and B.subtilis with respect to the enzymes which phosphorylate CMP are consistent with the measurements which indicate that turnover of messenger RNA is largely hydrolytic in E.coli but largely phosphorolytic in B.subtilis.