Interaction of Escherichia Coli RNA Polymerase with Promoters of Several Coliphage and Plasmid DNAs

The interaction of Escherichia coli RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) with restriction fragments obtained from various E. coli related DNAs was studied in vitro. The DNAs investigated included several coliphage genomes (T5, lambda, T7, fd) and plasmid DNAs (pML 21, pSC101). By using the nitrocellulose filter binding of the enzyme-DNA complexes, fragment-specific relative rates of complex formation as well as complex stabilities were determined. Promoter-specific relative rates of polymerase binding were derived from fragment-specific rates by taking into account the number of major binding sites for RNA polymerase within several DNAs. Estimates of the stability of complexes formed between some major binding sites and the enzyme were obtained by studying the rate of complex decay. Both characteristics--rate of complex formation and rate of decay--varied widely and independently of each other. The promoters reacting most efficiently with E. coli RNA polymerase were found in the early region of coliphage T5 whereas some promoters in pML 21, or for example, the lambda promoter PI, belong to signals binding the enzyme most slowly. Based on the second-order rate constant determined for the interaction of E. coli RNA polymerase with promoters of phage fd, the fastest promoters characterized so far reacted with rates in the order of 10(8) M-1s-1. The hierarchy of promoters established here is of interest from the viewpoint that promoter strength correlates with the rate of polymerase binding. Among the promoters studied here this rate spans a range of 2 orders of magnitude.