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Mini-P1 plasmid replication: the autoregulation-sequestration paradox

D K Chattoraj1, R J Mason, S H Wickner

  • 1Laboratory of Biochemistry, National Cancer Institute, Bethesda, Maryland 20892.

Cell
|February 26, 1988
PubMed

Insights

Initiator protein RepA controls mini-P1 plasmid replication. DNA looping by RepA simultaneously binding the control locus and promoter resolves the autoregulation-sequestration paradox, enabling repression.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • The initiator protein RepA is proposed as rate-limiting for mini-P1 plasmid replication.
  • Plasmid copy number control is thought to sequester RepA, reducing replication.
  • RepA autoregulation presents a paradox with sequestration, as lost protein should be replenished.

Purpose of the Study:

  • To resolve the paradox between RepA autoregulation and sequestration in mini-P1 plasmid replication control.
  • To investigate the mechanism by which sequestered RepA might still exert regulatory control.

Main Methods:

  • Demonstration of RepA binding to both the control locus and promoter region.
  • Observation of DNA looping induced by simultaneous RepA binding.

Main Results:

  • RepA binds simultaneously to the mini-P1 plasmid control locus and promoter region.
  • This simultaneous binding results in the looping of the intervening DNA.
  • DNA looping provides a mechanism for RepA to exert repression.

Conclusions:

  • RepA-mediated DNA looping resolves the autoregulation-sequestration paradox.
  • Sequestered RepA remains available for promoter repression, not just replication.
  • This mechanism explains how RepA controls plasmid copy number.

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