Transcription map of the early region of the Streptomyces bacteriophage φC31

Abstract

Streptomyces coelicolor A3(2), lysogenised by the temperature-sensitive c ts1 mutant of φC31, can be synchronously induced into the lytic cycle by heat treatment. A transcription map of 10 kb of the φC3l early gene cluster was deduced using low-resolution S1 nuclease mapping of RNA prepared 10 min after induction. At least nine early transcripts, early (e)RNAs 1-9, were localised reading exclusively rightwards with respect to the standard physical map of φC31. The mRNAs were extensively overlapping, frequently initiating at the same place but terminating at different sites, and vice versa. Gene expression during the lytic cycle was tightly regulated; no transcription was observed before induction. Transcription was maximal at 10 min post-induction, and at 20 min, eRNAs 5 and 6 persisted whilst eRNAs 7–9 were severely reduced or absent. The pattern of transcription of the early region is consistent with the simultaneous activation of a large number of promoters and differential termination efficiency.