Formation of poliovirus RNA polymerase 3D in Escherichia coli by cleavage of fusion proteins expressed from cloned viral cDNA.

The poliovirus polymerase 3D was synthesized in Escherichia coli by cleavage of fusion proteins expressed from cloned viral cDNA inserted into several plasmid expression vectors. Cleavage was accomplished by the action of viral protease 3C sequences expressed in the same bacteria, either from a second plasmid or from the same plasmid, cloned so as to produce contiguous sequences in the same protein. In the case of two plasmids, protease 3C functioned in trans to cleave the fusion protein at or very near the normal Gln/Gly cleavage site. When protease and polymerase sequences were produced in the same protein, the protease sequences acted in the precursor form to release the polymerase from itself. Thus, cleavage can occur to generate polymerase 3D both as an intermolecular reaction and, very likely, also as an intramolecular event.