Structural Properties of Escherichia coli RNA Polymerase Subunits

1 The surface of the RNA‐polymerase ‐ DNA complex possesses an exposed polypeptide loop. 2 Proteinases with differing specificities (trypsin, chymotrypsin, subtilisin and clostripain) preferentially cleave the exposed region. 3 The cleaved polypeptide is reassembled into RNA polymerase by renaturation from a solvent which promotes a random coil conformation. 4 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. 5 Isolated α subunits are comparatively resistant to proteolysis. 6 Although of similar molecular weights β and β′ appear to have unrelated primary sequences and markedly different conformations in free solution. 7 Digestion of the β subunit may be blocked by formation of the α 2 β subassembly. 8 Evidence is presented suggesting that β in the intact enzyme (α 2 ββ′) possesses the exposed polypeptide loop.