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Molecular analysis of RNAI control of repB translation in IncB plasmids

I W Wilson1, J Praszkier, A J Pittard

  • 1Department of Microbiology, University of Melbourne, Parkville, Victoria, Australia.

Journal of Bacteriology
|November 1, 1994
PubMed

Insights

This study reveals how RNAI controls IncB plasmid replication by regulating repA expression. RNAI primarily inhibits pseudoknot formation, not repB translation, to manage plasmid copy number.

Area of Science:

  • Molecular Biology
  • Microbiology
  • Genetics

Background:

  • IncB plasmid replication relies on the RepA protein.
  • RepA translation requires specific mRNA (RNAII) folding into a pseudoknot.
  • Leader peptide RepB translation and termination are crucial for pseudoknot formation.

Purpose of the Study:

  • To elucidate the regulatory mechanism of IncB plasmid pMU720 replication.
  • To determine the role of countertranscript RNAI in controlling repA expression.
  • To investigate the interplay between RNAI, RNAII, and RepB in plasmid replication.

Main Methods:

  • Analysis of mRNA-RNAI interactions.
  • Investigation of translational control mechanisms.
  • Assessment of plasmid copy number upon disruption of regulatory pathways.

Main Results:

  • RNAI negatively regulates repA expression by interacting with RNAII.
  • RNAI directly sequesters bases needed for pseudoknot formation.
  • RNAI indirectly inhibits RepB translation via steric hindrance near the initiation site.
  • Disrupting RNAI control of RepB had minimal impact on plasmid copy number.

Conclusions:

  • RNAI primarily controls IncB plasmid replication by inhibiting RNAII pseudoknot formation.
  • Inhibition of RepB translation is a secondary mechanism and less critical for copy number control.
  • The study clarifies the dominant role of pseudoknot formation inhibition in plasmid replication regulation.

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