Evidence of Protein Kinase Activity and Characterization of Substrate Proteins in Escherichia Coli
In contrast with eukaryotes which have long been known to harbor a variety of protein kinase activities, the occurrence of protein phosphorylation in bacteria has been, until recently, a matter of controversy. Thus, the phosphorylating activity originally described in Escherichia coli extracts1 was later found to be a polyphosphate kinase rather than a protein kinase2. Also, the protein kinase activity detected3 in bacteria after infection with bacteriophage T7 was shown to be specifically a viral gene product naturally absent in uninfected cells4. In other experiments5–7 no definite conclusion could be drawn mainly because of the incomplete chemical characterization of the phosphorylated moiety of proteins. From these observations it was then generally concluded that bacterial cells do not contain any protein kinase activity3,4. In recent years, however, this concept has been reversed by a number of unambiguous results which have brought conclusive evidence that protein phosphorylation does occur in E.coli 8,9. The purpose of this article is to briefly summarize these results and to present in more detail some recent developments in the field.
KeywordsProtein Phosphorylation Isocitrate Dehydrogenase Amino Acid Starvation Strain CP78 Phosphoamino Acid
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