The role of the chromatin-associated protein Hbsu in β-mediated DNA recombination is to facilitate the joining of distant recombination sites |
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Authors: | Juan C Alonso Crisanto Gutierrez Fernando Rojo |
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Institution: | Centro Nacional de Biotecnología, C.S.I.C., Campus Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain; Centro de Biología Molecular 'Severe Ochoa', C.S.I.C., Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain |
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Abstract: | The β recombinase is unable to mediate in vitro DNA recombination between two directly oriented recombination sites unless a bacterial chromatin-associated protein ( Bacillus subtilis Hbsu or Eschrichia coli HU) is provided. By electron microscopy, we show that the role of Hbsu is to help in joining the recombination sites to form a stable synaptic complex. Some evidence supports the fact that Hbsu works by recognizing and stabilizing a DNA structure at the recombination site, rather than by serving as a bridge between β recombinase dimers through a protein-protein interaction. We show that the mammalian HMG1 protein, which shares neither sequence nor structural homology with Hbsu, can also stimulate β-mediated recombination. These chromatin-associated proteins share the property of binding to DNA in a relatively non-specific fashion, bending it, and having a marked preference for altered DNA structures. Hbsu, HU or HMG1 proteins probably bind specifically at the crossing-over region, since at limiting protein-DNA molar ratios they could not be outcompeted by an excess of a DNA lacking the crossing over site. Distamycin, a minor groove binder that induces local distortions in DNA, did not affect the binding of β protein to DNA, but inhibited the formation of the synaptic complex. |
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