As in eukaryotes, phosphorylation of Ser and Thr residues in proteins appears to be a common phenomenon in bacteria. Surprisingly, however, very few Ser/Thr protein kinases have been identified and in this study antibodies directed against mammalian protein kinase C (PKC) have been used in attempts to isolate conserved Ser/Thr protein kinases. Using the mAb M7 against rat brain PKC, a single 70 kDa band was identified in total cell extracts of by Western blotting after SDS-PAGE, whilst using polyclonal antibody α-PKC1p against PKC a single 67 kDa band was identified by the same procedure. The two proteins were purified independently on the basis of antibody recognition employing two-dimensional gel electrophoresis as a final step, which allowed subsequent microsequencing. The 70 kDa band was thus identified as the phosphoenolpyruvate-dependent His HPr kinase. Enzyme I of the phosphotransferase system. This identity was confirmed using a mutant deleted for encoding Enzyme I. The 67 kDa protein was identified as a previously unknown “trigger factor”, homologous to an protein-folding enzyme, peptidylprolyl -isomerase implicated in cell division.


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