Control of promoter utilization by bacteriophage T4-induced modification of RNA polymerase alpha subunit

After infection of Escherichia coli cells, bacteriophage T4 induces several changes in the host DNA-dependent RNA polymerase. A well-characterized chemical change is a two-step ADP-ribosylation of the enzyme's alpha subunit (1). In order to investigate the effect of this change on RNA polymerase transcriptional properties in an in vitro system, we have reconstituted the enzyme from separated individual subunits which were obtained from normal or T4-modified RNA polymerases. It is demonstrated that the enzymes containing T4-modified alpha differ from the enzymes with normal alpha in two respects: (i) their overall activity on T4 DNA is reduced and (ii) they fail to utilize certain T4 promotors while efficiently utilizing other promoters. Among the promoters which are switched off by alpha modification are the two promoters of the D region and one of the two promoters of the T4 tRNA gene cluster. The differential effect of alpha modification on the expression of the tRNA and the D regions in vitro correlates with the previously established pattern of their transcription in vivo. It is suggested that the T4-induced ADP-ribosylation of RNA polymerase alpha subunit is involved in the shutoff of the early bacteriophage genes at the late stage of phage development.