Structure of helical RecA-DNA complexes. III. The structural polarity of RecA filaments and functional polarity in the RecA-mediated strand exchange reaction |
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| Authors: | A Stasiak E H Egelman P Howard-Flanders |
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| Institution: | Institute for Cell Biology, E.T.H. Honggerberg, Zurich, Switzerland. |
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| Abstract: | The RecA protein of Escherichia coli has been used in vitro to mediate a strand-exchange reaction between homologous DNA molecules. A three-dimensional reconstruction of a RecA filament on double-stranded DNA has been previously determined from electron micrographs, and the reconstruction displays a clear axial polarity. The RecA-mediated strand-exchange reaction between a double-stranded DNA and a homologous single-stranded DNA that is complexed with a RecA helical polymer proceeds with a known polarity. Using image analysis of electron micrographs, we have determined the relation between the structural polarity of RecA filaments and the 3' and 5' polarity of single-stranded DNA. Thus, the structural polarity of RecA filaments can now be related to the direction in which the RecA-mediated strand-exchange reaction advances along the complexed single-stranded DNA. |
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