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Related Experiment Videos

Repression of the lambda pcin promoter by integrative host factor.

G Griffo1, A B Oppenheim, M E Gottesman

  • 1Institute of Cancer Research, Columbia University, New York, NY 10032.

Journal of Molecular Biology
|September 5, 1989
PubMed
Summary

Integrative host factor (IHF) represses bacteriophage lambda

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Area of Science:

  • Molecular Biology
  • Genetics
  • Virology

Background:

  • The cin-1 mutation in bacteriophage lambda introduces a novel promoter, pcin, in the tR1 region.
  • This pcin promoter constitutively transcribes the cI repressor gene.

Purpose of the Study:

  • To investigate the role of Integrative Host Factor (IHF) in regulating the activity of the pcin promoter.
  • To determine if IHF acts as a repressor of pcin transcription.

Main Methods:

  • Bacteriophage lambda propagation in Escherichia coli mutants lacking IHF.
  • In vitro transcription assays, including abortive initiation and gel retardation assays.
  • Analysis of RNA polymerase binding to the pcin promoter in the presence and absence of IHF.

Main Results:

  • Bacteriophage lambda cin-1 exhibits impaired propagation in IHF-deficient E. coli, suggesting repressor overproduction inhibits lytic growth.
  • The pcin promoter shows a fivefold increase in activity in IHF-deficient hosts compared to wild-type.
  • In vitro studies confirm that IHF directly inhibits transcription initiation at the pcin promoter.
  • IHF interferes with RNA polymerase binding to the pcin promoter, but not with an open promoter complex.

Conclusions:

  • IHF functions as a repressor of the pcin promoter in bacteriophage lambda.
  • IHF binding to the pcin promoter region likely hinders RNA polymerase binding, either through direct nucleotide blocking or DNA distortion.
  • This mechanism explains the impaired lytic growth of lambda cin-1 in IHF-deficient hosts.

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