Transcription termination sites in the major leftward operon of coliphage lambda

Abstract

A transcriptional mapping technique was employed to determine the locations of leftward transcription termination sites within the p L- att region of bacteriophage λ. Lysogens in which phage or host mutations blocked N-mediated antitermination were used. The results are consistent with the presence of three major termination sites, designated t L1, t L2, and t L3, which map at about 71.1 (between genes N and ral), 68.9 (likely within gene cIII) and 64.4 (within gene exo) %λ units, respectively, measured from the left terminus of the mature λ DNA. The t L1 terminator is about 80% efficient, while the t L2 and t L3 terminators are over 90% efficient. The locations of other possible terminators, including one near the nutL site and another within the int gene, are also discussed.