IDENTIFICATION OF PHOSPHOPROTEINS IN ESCHERICHIA-COLI

The substrates of ion- and lipid-stimulated protein kinase activity in extracts of Escherichia coli were purified by chromatography. Subsequ ent N-terminal sequencing suggests that these substrates include the f ollowing: a novel 80kDa protein co-purifying with RNA polymerase but p artially homologous to elongation factor G; a protein with an apparent molecular weight of 65kDa identified as the ribosomal protein S1; and a 32kDa protein identified as succinyl CoA synthetase, a key enzyme i n the tricarboxylic acid cycle. The phosphorylation of these three pro teins was markedly stimulated by the addition of manganese, and occurr ed on threonine, serine or tyrosine residues as indicated by the stabi lity of the phosphoresidues during acid treatment. In addition, a calc ium-stimulated protein of 70kDa was identified as the heat-shock prote in DnaK, and a 17kDa lipid-stimulated phosphoprotein as nucleotide dip hosphate kinase.