Release of polarity in Escherichia coli by gene N of phage lambda: termination and antitermination of transcription.

The induction of lambda prophage provokes the constitutive expression of the adjacent gal operon in E. coli. This "escape synthesis" can result from transcription that initiates at a phage promoter and extends into the gal operon. The effect requires the product of the lambda gene N. N-mediated transcription not only fails to terminate at the prophage-bacterial junction and at the ends of bacterial operons, but ignores termination signals caused by polar insertions or ochre mutations within gal. Suppression of polarity by N-function is a cis-effect; only transcription initiated at the phage promoter is influenced. We propose that the transcription complex is influenced by N-product to become termination-resistant at a site in the phage genome (juggernaut model). This site appears to be at or near the phage promoter.