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Repressor CopG prevents access of RNA polymerase to promoter and actively dissociates open complexes

Ana M Hernández-Arriaga1, Tania S Rubio-Lepe, Manuel Espinosa

  • 1Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.

Nucleic Acids Research
|June 13, 2009
PubMed

Insights

The repressor CopG protein controls plasmid pMV158 replication by inhibiting RNA polymerase binding and displacing it from the promoter P(cr). This reveals a dual mechanism for transcriptional repression.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Plasmid pMV158 replication depends on the repB initiator gene, regulated by the CopG repressor.
  • The repB and copG genes are co-transcribed from the P(cr) promoter.

Purpose of the Study:

  • To investigate the mechanism of transcriptional repression by CopG at the P(cr) promoter.
  • To understand the interactions between RNA polymerase, CopG, and the P(cr) promoter DNA.

Main Methods:

  • Comparative analysis of RNA polymerase-P(cr) complexes formed at different temperatures (0°C and 37°C).
  • Investigation of CopG's effect on RNA polymerase binding and stable complex formation at P(cr).

Main Results:

  • RNA polymerase-P(cr) complexes exhibit distinct stability and DNA contact extent at 0°C versus 37°C.
  • The stable 37°C complex, with a 3-hour half-life, shares characteristics with typical open promoter complexes.
  • CopG represses transcription by preventing initial RNA polymerase binding and by actively displacing pre-formed stable complexes.

Conclusions:

  • CopG employs a dual mechanism to repress transcription initiation at P(cr).
  • CopG hinders RNA polymerase recruitment and can disassemble stable RNA polymerase-promoter complexes.
  • A model for CopG-mediated disassembly of the RNA polymerase-P(cr) complex is proposed.

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