EXPRESSION AND CHARACTERIZATION OF PHOSPHORYLATED RECOMBINANT HUMAN BETA-CASEIN IN ESCHERICHIA-COLI

Specific serine and threonine residues of recombinant human beta-casei n produced in Escherichia coil were shown to be phosphorylated in vivo when human casein kinase II was coexpressed in the same plasmid. All of the phosphorylated forms found in the native protein were also dete cted in the recombinant protein. The phosphorylation of recombinant hu man beta-casein was confirmed by immunoblots, fast protein liquid chro matography, urea-polyacrylamide gel electrophoresis, SDS-polyacrylamid e gel electrophoresis, and liquid chromatography-mass spectrometry. Th e results indicate that the substrate specificity of casein kinase II in vivo was unaffected in its recombinant form. This is the first demo nstration of in vivo phosphorylation of specific residues of a multiph osphorylated protein produced in E. coil with a single plasmid. (C) 19 97 Academic Press.