title: Mini-P1 plasmid replication: the autoregulation-sequestration paradox.
abstract: It has been proposed that the initiator protein RepA is rate limiting for mini-P1 plasmid replication, and that the role of the plasmid copy number control locus is to sequester the initiator and thus reduce replication. This proposal appears inconsistent with the observation that RepA is autoregulated, since the protein lost by sequestration should be replenished. A resolution of this autoregulation-sequestration paradox is possible if the sequestered RepA, unavailable for replication, is still available for promoter repression. We demonstrate that RepA binds to the control locus and to the promoter region simultaneously, causing the intervening DNA to loop. DNA looping could provide the requisite mechanism by which RepA bound to the control locus might exert repression.
authors.affiliation: Laboratory of Biochemistry, National Cancer Institute, Bethesda, Maryland 20892.
authors.forename: D K
authors.initials: DK
authors.lastname: Chattoraj
authors.forename: R J
authors.initials: RJ
authors.lastname: Mason
authors.forename: S H
authors.initials: SH
authors.lastname: Wickner
mesh_terms: D004265:DNA Helicases; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics; D005786:Gene Expression Regulation; D008854:Microscopy, Electron; D009690:Nucleic Acid Conformation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011506:Proteins; D012097:Repressor Proteins / Q000502:physiology*; D015534:Trans-Activators; D014157:Transcription Factors / Q000502:physiology*; D014764:Viral Proteins / Q000502:physiology*
chemical_list: D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D011506:Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D014764:Viral Proteins; C045264:replication initiator protein; D004265:DNA Helicases