title: Electron microscopic visualization of recA-DNA filaments: evidence for a cyclic extension of duplex DNA.
abstract: As visualized by electron microscopy, RecA protein binds in a highly cooperative manner to single-stranded fd DNA in solutions of 0.01 M Tris (pH 7.5). The resulting nucleoprotein filament loops are 1.25 micrometers in length, have a fiber diameter of 12 nm and show an indication of a 4.5 nm repeat along the axis of the compact fibers. RecA binds to linear duplex fd DNA in solutions of 0.01 M Tris (pH 7.5) to yield chains of beads which, in the presence of Mg2+ and ATP, coalesce into smooth filaments with a length of 1.9 micrometers (the length of protein-free fd duplex DNA) and have a fiber diameter of 12 nm. In solutions containing Mg2+ and ATP-gamma-S, however, RecA binds to duplex DNA in a highly cooperative manner to yield rigid filaments 3.0 micrometers in length. These filaments are 12 nm in diameter and show a very clear 7.5 nm axial repeat. This extension of DNA to 150% of its usual length in the apparent absence of any single-stranded components suggests that the DNA helix must also be highly unwound and provides new insights into the mode of RecA action.
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D001426:Bacterial Proteins / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D008274:Magnesium / Q000378:metabolism; D008854:Microscopy, Electron; D008954:Models, Biological; D009698:Nucleoproteins / Q000378:metabolism; D011938:Rec A Recombinases; D012093:Replicon; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D009698:Nucleoproteins; D013873:Thionucleotides; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D011938:Rec A Recombinases; D008274:Magnesium