In fact, the two major classes of chromosomal lesions are recognized and processed by the two individual pathways at the early phase of homologous recombination. At the same time, the mechanisms of homologous recombination are uniquely suited for repair of complex DNA lesions called chromosomal lesions. All this complexity is incongruent with the originally ascribed role of homologous recombination as accelerator of genome evolution: there is simply not enough duplication and repetition in enterobacterial genomes for homologous recombination to have a detectable evolutionary role, and therefore not enough selection to maintain such a complexity. coli, there are at least two independent pathway of the early phase and at least two independent pathways of the late phase. Genetic analysis of homologous recombination reveals three separate phases of this process: pre-synapsis (the early phase), synapsis (homologous strand exchange) and post-synapsis (the late phase). coli and Salmonella to detect homologous recombination events of several different kinds. There is a variety of experimental systems in E. Homologous recombination events are exchanges between DNA molecules in the lengthy regions of shared identity, catalyzed by a group of dedicated enzymes. The same contacts are seen to be skewed in projection for the antiparallel molecules.Homologous recombination is the most complex of all recombination events that shape genomes and produce material for evolution. Also note that the symmetry brings symmetrically related portions of backbones into apposition along the center lines in parallel molecules, in these projections. Note the differences between the central portions of DPOW and DPON. An attempt has been made to portray the differences between the major and minor grooves. Here, the blue strands are related to the red strands by the dyad axis lying horizontal on the page. The 5' end of the central green double crossover strand is related to the 3' end by the same dyad element. The twofold axis perpendicular to the page (DAE) relates the two red helical strands to each other, and the two blue outer crossover strands to each other. In the case of the parallel strands, the red strands are related to the other red strands by the twofold axes vertical on the page similarly, the blue strands are symmetrically related to the blue strands. The strands have been drawn with pens of two different colors (three for DAE), as an aid to visualizing the symmetry. Note that the dyad in DAE is only approximate, because the central strand contains a nick, which destroys the symmetry. The structures contain implicit symmetry, which is indicated by the conventional markings, a lens-shaped figure (DAE) indicating a potential dyad perpendicular to the plane of the page, and arrows indicating a twofold axis lying in the plane of the page. The arrowheads at the ends of the strands designate their 3' ends. The strands are drawn as zig-zag helical structures, where two consecutive, perpendicular lines correspond to a full helical turn for a strand. The extra half-turn can correspond to a major (wide) groove separation, designated by 'W', or an extra minor (narrow) groove separation, designated by 'N'. A fourth character is needed to describe parallel double crossover molecules with an odd number of helical half-turns between crossovers. ![]() The third character refers to the number (modulus 2) of helical half-turns between crossovers, 'E' for an even number and 'O' for an odd number. The second character refers to the relative orientations of their two double helical domains, 'A' for antiparallel and 'P' for parallel. All names begin with 'D' for double crossover. The structures shown are named by the acronym describing their basic characteristics. Double crossover molecules Double Crossover Molecules
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