DNA looping can enhance lysogenic CI transcription in phage lambda

L. Meadow Anderson, Haw Yang

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


The lysogenic state of bacteriophage lambda is maintained by CI repressor, which negatively regulates two promoters to block lytic gene expression. Expression of CI is itself controlled by positive and negative feedback as CI binds to OR to regulate the PRM promoter. In addition to direct interactions with operator DNA, CI tetramers bound at OL and OR can come together to form an octamer, looping the DNA that lies between them and allowing OL to assist with negative regulation of PRM. We used a fluorescent reporter protein to measure the CI concentration for a set of constructs that differ in their ability to assume various forms of the looped structure. Based on the observed steady-state fluorescence for these constructs, the presence of OL increases PRM activation unless both operators can be fully occupied. By calculating the probabilities for the underlying operator configurations present in each construct, two different models for the mechanism of enhanced activation allow us to predict that when the DNA is looped, PRM activation can be 2- to 4-fold higher than is possible for unlooped DNA. Based on our results, transcriptional regulation for lambda's lysogenic/lytic switch includes both activation and repression due to DNA looping.

Original languageEnglish (US)
Pages (from-to)5827-5832
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number15
StatePublished - Apr 15 2008
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General


  • Bacteriophage lambda
  • Flow cytometry
  • Gene regulation


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