Structural Properties of Escherichia coli RNA Polymerase Subunits

The surface of the RNA‐polymerase ‐ 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 β subunit has a proteolytically resistant nucleus of approximately 70000 molecular weight. This resistant polypeptide may be generated by trypsin, chymotrypsin, subtilisin or clostripain. Isolated α subunits are comparatively resistant to proteolysis. Although of similar molecular weights β and β′ appear to have unrelated primary sequences and markedly different conformations in free solution. Digestion of the β subunit may be blocked by formation of the α 2 β subassembly. Evidence is presented suggesting that β in the intact enzyme (α 2 ββ′) possesses the exposed polypeptide loop.