Nucleoprotein architecture and ColE1 dimer resolution: a hypothesis.
Dimers of plasmid ColE1 are converted to monomers by site-specific recombination, a process that requires 240 bp of DNA (cer) and four host-encoded proteins (XerC, XerD, ArgR and PepA). Here, we propose structures for nucleoprotein complexes involved in cer-Xer recombination based upon existing knowledge of the structures of component proteins and computational analyses of protein structure and DNA curvature. We propose that, in the nucleoprotein complex at a single cer site, a PepA hexamer acts as an adaptor, connecting the heterodimeric recombinase (XerCD) to an ArgR hexamer. This provides a protein core around which the cer site wraps, its exact path being defined by strong sequence-specific interactions with ArgR and XerCD, weak interactions with PepA and sequence-dependent flexibility of cer. The initial association of single-site complexes (pairing) is proposed to occur via an ArgR-PepA interaction. Pairing between sites in a plasmid dimer is stabilized by DNA supercoiling and is followed by a structural isomerization to form a recombination-proficient synaptic complex. We propose that paired structures formed between sites in trans are too short-lived to permit synaptic complex formation. There is thus an energetic barrier to inappropriate recombination reactions. Our proposals are consistent with a wide range of experimental observations.
Department of Genetics, University of Cambridge, UK.
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D000123:Acetyltransferases / Q000737:chemistry / Q000378:metabolism; D051046:Amino-Acid N-Acetyltransferase; D000626:Aminopeptidases / Q000737:chemistry* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004254:DNA Nucleotidyltransferases / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D043384:Glutamyl Aminopeptidase; D019426:Integrases / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009698:Nucleoproteins / Q000737:chemistry* / Q000378:metabolism; D010957:Plasmids / Q000737:chemistry* / Q000235:genetics; D045522:Recombinases
D009698:Nucleoproteins; D045522:Recombinases; D000123:Acetyltransferases; D051046:Amino-Acid N-Acetyltransferase; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C115006:integron integrase IntI1; D000626:Aminopeptidases; D043384:Glutamyl Aminopeptidase