Expression of the polyoma middle-size T antigen in Escherichia coli.

We constructed a plasmid encoding a hybrid protein, consisting of the N-terminal signal sequence of the major outer membrane lipoprotein (lpp) of Serratia marcescens joined to the polyoma middle-size T antigen (mT antigen). The hybrid protein expressed under the control of a lpp-lac hybrid promoter was synthesized at levels up to 5% of newly synthesized protein and could be accumulated in Escherichia coli strains carrying the Cap R mutation. The mT antigen produced in E. coli was precipitated by polyoma antitumor serum, and by serum directed against a synthetic peptide corresponding to the C terminus of the authentic mT antigen. The protein was secreted into the periplasmic space, from which it could be released by osmotic shock. The bacterial mT antigen had no detectable associated protein kinase activity.