Structural Properties of Escherichia coli RNA Polymerase Subunits

Abstract
The surface of the RNA-polymerase.cntdot.DNA complex possesses an exposed polypeptide loop. Proteinases with differing specificities (trypsin, chymotrypsin, subtilisin and clostripain) preferentially cleave the exposed region. The cleaved polypeptide is reassembled into RNA polymerase by renaturation from a solvent which promotes a random coil conformation. Isolated .beta. subunit has a proteolytically resistant nucleus of approximately 70,000 MW. This resistant polypeptide may be generated by trypsin, chymotrypsin, subtilisin or clostripain. Isolated .alpha. subunits are comparatively resistant to proteolysis. Although of similar MW''s, .beta. and .beta.'' appear to have unrelated primary sequences and markedly different conformations in free solution. Digestion of the .beta. subunit may be blocked by formation of the .alpha.2.beta. subassembly. .beta.'' in the intact enzyme (.alpha.2.beta..beta.'') may possess the exposed polypeptide loop.