Related Experiment Video
Updated: Oct 18, 2026

Understanding the Impact of Temperate Bacteriophages on Their Lysogens Through Transcriptomics
Published on: January 5, 2024
Constitutive expression of a transcription termination factor by a repressed prophage: promoters for transcribing the
R A King1, P L Madsen, R A Weisberg
1Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA. rking@lmgvax.nichd.nih.gov
Abstract:
Lysogens of phage HK022 are resistant to infection by phage lambda. Lambda resistance is caused by the action of the HK022 Nun protein, which prematurely terminates early lambda transcripts. We report here that transcription of the nun gene initiates at a constitutive prophage promoter, P(Nun), located just upstream of the protein coding sequence. The 5' end of the transcript was determined by primer extension analysis of RNA isolated from HK022 lysogens or RNA made in vitro by transcribing a template containing the promoter with purified Escherichia coli RNA polymerase. Inactivation of P(Nun) by mutation greatly reduced Nun activity and Nun antigen in an HK022 lysogen. However, a low level of residual activity was detected, suggesting that a secondary promoter also contributes to nun expression. We found one possible secondary promoter, P(Nun)', just upstream of P(Nun). Neither promoter is likely to increase the expression of other phage genes in a lysogen because their transcripts should be terminated downstream of nun. We estimate that HK022 lysogens in stationary phase contain several hundred molecules of Nun per cell and that cells in exponential phase probably contain fewer.
Related Concept Videos
Prokaryotic Transcriptional Activators and Repressors
Transcription of prokaryotic...
Prokaryotic Transcriptional Activators and Repressors
Transcription of prokaryotic...
Transcription Attenuation in Prokaryotes
There are several different mechanisms used to attenuate transcription. In ribosome mediated...
Bacterial Transcription
Transcription can be divided into three main stages, each involving distinct DNA sequences to guide the polymerase. These are:
Transcription in Prokaryotes
Constitutive and Regulated Gene Expression

