RNA metabolism in T4-infected Escherichia coli

Abstract

Discrete species of 14C-labeled messenger RNA from T4-infected Escherichia coli can be detected as bands on polyacrylamide gels after electrophoresis and autoradiography. Experiments are presented which demonstrate that the transcriptional patterns change during the course of infection and that protein synthesis inhibition at appropriate times of infection prevents certain transcriptional transitions. It is shown that the synthesis of stable host RNA (23 s, 16 s, 5 s and transfer RNA) ceases after two minutes of infection at 25 °C but that the addition of chloramphenicol to the culture before infection prevents this shut off. “Early” phage RNA which is synthesized before the onset of DNA synthesis can be divided into two subclasses by virtue of the fact that only one class is synthesized in chloramphenicol pretreated cultures. Also, chloramphenicol prevents the synthesis of late phage RNA even if added at a time when it allows a significant amount of phage DNA to be synthesized. This indicates that phage DNA synthesis is a necessary but not a sufficient requirement for transcription of the late phage genes. Analysis of the RNA synthesized by cultures infected with various phage mutants demonstrates that phage DNA synthesis and the functioning of genes 55 and 33 are required for the synthesis of late messenger RNA which is synthesized after 20 minutes of infection at 25 °C. The striking similarity of the RNA patterns from cultures infected with amber mutants in genes 33 and 55 corroborates their classification in the same class of maturation defectiveness. It is shown that though almost all of the RNA labeled during phage infection is unstable, several RNA species in the molecular weight range 20,000 to 50,000 are stable and accumulate in large amounts during infection. The results are discussed in relation to our current understanding of the mechanisms controlling RNA and protein synthesis in phage-infected cells.