Synthesis of phage- and host-specific RNA in Escherichia coli infected with a fragment of bacteriophage T5

Abstract

Escherichia coli F bacteria were infected with an amber mutant of phage T5, which injects only 8% (the pre-early genes) of its genome into the host cell. This system allows study of the simultaneous transcription of host and phage DNA for an extended period of time. With increasing multiplicity of infection, the fraction of phage-specific RNA increases from 0.03 at m.o.i. = 1 to 1.0 m.o.i. →∞, while the fractional synthesis of bacterial RNA decreases correspondingly. This indicates that the pre-early T5 promoters compete with bacterial promoters for RNA polymerase. With increasing multiplicity, the synthesis rates of host mRNA and stable RNA (rRNA and tRNA) decrease in constant proportions. At low multiplicities, when the synthesis of phage RNA is proportional to the number of infecting phage, the initiation frequency at the average pre-early T5 promoter is 30 RNA chains/min; this promoter activity is comparable to that of bacterial rRNA promoters.