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Structural basis of Q-dependent antitermination.

Zhou Yin1,2, Jason T Kaelber3,4, Richard H Ebright5,2

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Summary

Bacteriophage Q protein enables gene expression by guiding RNA polymerase past transcription terminators. Structural studies reveal Q forms a "nozzle" that prevents hairpin formation, ensuring antitermination.

Keywords:
RNA polymerasetranscription antiterminationtranscription antitermination factor Qtranscription antitermination factor Q21transcription elongation complex

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Virology

Background:

  • Bacteriophage Q protein is essential for switching gene expression from middle to late stages.
  • This switch is achieved by enabling RNA polymerase (RNAP) to read through transcription terminators.
  • Q protein interacts with RNAP at promoter-proximal pausing sites, including the Q binding element (QBE) and sigma-dependent pause element (SDPE).

Purpose of the Study:

  • To elucidate the structural mechanisms by which bacteriophage Q protein mediates transcriptional antitermination.
  • To determine high-resolution structures of key states in the Q protein antitermination pathway.

Main Methods:

  • X-ray crystallography was used to determine the structures of Q protein and its complexes with RNAP.
  • Four distinct structural states were resolved: Q protein alone, the Q-QBE complex, the Q-loading complex, and the Q-loaded complex.

Main Results:

  • The structures reveal that Q protein forms a toroidal "nozzle" that engages with the RNAP RNA-exit channel.
  • This interaction narrows and extends the channel, extruding single-stranded RNA.
  • The Q21 protein structure prevents the formation of critical pause and terminator hairpins within the RNA.

Conclusions:

  • Bacteriophage Q protein employs a unique structural mechanism to ensure transcriptional antitermination.
  • The Q protein "nozzle" effectively remodels the RNAP active site to facilitate read-through transcription.
  • These findings provide atomic-level insights into a crucial viral gene regulation strategy.