The process of infection with coliphage T7: III. Control of phage-specific RNA synthesis in vivo by an early phage gene

After infection of Escherichia coli with bacteriophage T7, 12 or 13 new phage-specific RNA species are synthesized. These are resolvable as discrete bands by polyacrylamide-agarose gel electrophoresis. Initiation of all T7 RNA species occurs to some extent before the onset of phage DNA synthesis. Only four of the normal T7 RNA's are made if phage-specific protein synthesis is blocked with chloramphenicol or kanamycin and one of these RNA's (mol. wt 1.1 × 10⁶) is probably the messenger RNA from gene 1. RNA made after infection with T7 carrying amber mutations in gene 1 has only three discrete species of T7 messenger RNA's. The RNA from cells infected with T7⁺ in the presence of 400 μg chloramphenicol/ ml. is very similar to T7 am23 (gene 1) RNA as judged by electrophoretic analysis and by RNA-DNA hybridization competition experiments. On the other hand, RNA made after infection with T7 carrying amber mutations in other genes is very similar to T7⁺ RNA. This result parallels that reported on the control of T7 protein synthesis which showed that the gene 1 protein controlled the production of all or nearly all other T7-induced proteins. These results suggest that while gene 1 is transcribed in the absence of phage protein synthesis, the gene 1 protein is required to transcribe the remainder of the T7 genome. The control of T7 protein synthesis is therefore mediated at the level of transcription by means of positive regulation.