Differential modes of processing and decay for the major N-dependent RNA transcript of coliphage λ

Abstract

The major leftward, N-dependent RNA synthesized from the p L (leftward promoter)- att operon of bacteriophage λ in wild-type and rivonuclease III (RNase III)-deficient hosts has been investigated by transcriptional mapping analysis. These studies reveal a sequence-specific program of post-transcriptional events leading to differential modes of RNA processing and decay of the N-dependent ( l′ 3) RNA transcript. The initial events, which comprise the RNA processing (rapid) phase, include RNase III-mediated cleavage of the p L-proximal l° i (containing the 5′-ppp terminus) and the next adjacent l 1 RNA species (both about 4.5 S in size) and a third cleavage event in the vicinity of the leftward transcriptional termination signal ( t L1) just to the left of gene N. This latter cleavage appears to be responsible for the differentially rapid decay of the gene N RNA segment derived from the 3′-end of l 1l -to- lt L1. This series of events is completed by the time the N-dependent transcription is terminated at the att site. The events of the succeeding secondary (relatively slow) phase are associated with the remaining t L1- att ( l 3 RNA) segment and comprise the initiation of endonucleolytic cleavage and subsequent chemical decay events which result in the uniform decay of the entire l 3 RNA segment of the l′ 3 RNA transcript.