CONTROL OF RIGHTWARD TRANSCRIPTION IN COLIPHAGE-LAMBDA BY THE REGULATORY FUNCTIONS OF PHAGE GENES-N AND GENES-CRO

Controls of rightward transcription, initiated at the pR and the p′R promoters of induced λ lysogen, were studied by employing RNA-DNA hybridization techniques. Transcription initiated at the pR promoter is partially turned off by the cro gene product shortly after induction. However, this turn-off appears to depend on certain functions specified by the gene N product, since no such turnoff is observed in λN-cro+ lysogens. Furthermore, the product of gene N, in addition to its known antitermination effect at tR1, is found to stimulate pR-promoted transcription in the pR-cro region that is located upstream from both the N utilization site, nutR, and terminator tR1. Thus, the regulation of pR-promoted transcription by the N and cro products is analogous to that of PL-promoted transcription; we propose that similar mechanisms may be involved in the regulation of these transcripts. This study also indicates that the regulatory effect of the cro product is required for normal transcription from the p′R(pQ) promoter, since a reduced rate of transcription in the p′R-S-J region is observed in λcro- lysogens. This late regulatory effect of the cro product must be mediated through the phage DNA replication functions, because when λ replication is blocked by a P mutation, the cro product no longer stimulates p′R-promoted transcription. These results indicate that complex interactions between the transcriptional functions, including the regulatory products of N and cro, and the components of the replication machinery are involved in the control of the orderly development of phage λ. © 1979.