Electron microscopic visualization of the RecA protein-mediated pairing and branch migration phases of DNA strand exchange.
The RecA protein of Escherichia coli will drive the pairing and exchange of strands between homologous DNA molecules in a reaction stimulated by single-stranded binding protein. Here, reactions utilizing three homologous DNA pairs which can undergo both paranemic and plectonemic joining were examined by electron microscopy: supertwisted double-stranded (ds) DNA and linear single-stranded (ss) DNA, linear dsDNA and circular ssDNA, and linear dsDNA and colinear ssDNA. Several major observations were: (i) with RecA protein bound to the DNA, plectonemic joints were ultrastructurally indistinguishable from paranemic joints; (ii) complexes which appeared to be joined both paranemically and plectonemically were present in these reactions in roughly equal numbers; and (iii) in complexes undergoing strand exchange, both DNA partners were often enveloped within a RecA protein filament consisting of hundreds of RecA protein monomers and several kilobases of DNA. These observations suggest that, following RecA protein-ssDNA filament formation, strand exchange proceeds by a pathway that can be divided structurally into three phases: pairing, envelopment/exchange, and release of the products.
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D001482:Base Composition; D004247:DNA / Q000378:metabolism / Q000648:ultrastructure; D004269:DNA, Bacterial / Q000378:metabolism / Q000648:ultrastructure*; D004270:DNA, Circular / Q000378:metabolism / Q000648:ultrastructure; D004277:DNA, Single-Stranded / Q000378:metabolism / Q000648:ultrastructure; D004278:DNA, Superhelical / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000235:genetics / Q000648:ultrastructure*; D008854:Microscopy, Electron; D008957:Models, Genetic; D011938:Rec A Recombinases / Q000378:metabolism*; D011995:Recombination, Genetic; D012689:Sequence Homology, Nucleic Acid
D004269:DNA, Bacterial; D004270:DNA, Circular; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004247:DNA; D011938:Rec A Recombinases