Bacteriophage-induced DNA-dependent RNA Polymerases

Abstract

INTRODUCTION In 1970, Chamberlin, McGrath and Waskell were able to show that the rifampicin-resistant RNA synthesis observed several minutes after infection of E. coli with phage T7 was not due to a modification of the host polymerase by a phage-specific σ factor, as had been assumed originally (Summers and Siegel 1969), but rather to an entirely new RNA polymerase, the product of the T7 early gene 1. The realization that this enzyme consisted of only one type of polypeptide chain and was probably active as a monomer made it an interesting object of study, especially for the purpose of comparing it with the much larger host RNA polymerase that had just then been discovered to be composed of at least five subunits, four of which being nonidentical (Burgess et al. 1969; Burgess 1969). Because of the selective role of the E. coli σ subunit in the initiation reaction and its elimination during chain elongation, it was thought that on the basis of the two types of reactions, RNA polymerase in general had to exist in two conformational states, with the σ protein acting as an allosteric effector. The sudden availability of a single-subunit RNA polymerase prompted the interesting question of whether such an enzyme would initiate RNA chains by a mechanism similar to or different from that of the multisubunit bacterial enzyme. Thus it was hoped that a comparative study of the two enzymes would shed additional light on the function of both enzymes. In this review I shall try...