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Holliday junction
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A Holliday junction is a branched nucleic acid structure that contains four double-stranded arms joined. These arms may adopt one of several conformations depending on buffer salt concentrations and t
Molecular structure of a stacked Holliday junction, in which the four arms stack into two double-helical domains. Note how the blue and red strands re
Molecular structure of a stacked Holliday junction, in which the four arms stack into two double-helical domains. Note how the blue and red strands remain roughly helical, while the green and yellow strands cross over between the two domains.
Diagrams of a tensegrity triangle complex containing three Holliday junctions, both in isolation (a) and as part of a crystal (b, c). In addition to t
Diagrams of a tensegrity triangle complex containing three Holliday junctions, both in isolation (a) and as part of a crystal (b, c). In addition to the two-dimensional array shown, this structure is capable of forming three-dimensional crystals.
Homologous recombination
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Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids.
Figure 2. An early illustration of crossing over from Thomas Hunt Morgan
Figure 2. An early illustration of crossing over from Thomas Hunt Morgan
Figure 11. As a developing embryo, this chimeric mouse had the agouti coat color gene introduced into its DNA via gene targeting. Its offspring are ho
Figure 11. As a developing embryo, this chimeric mouse had the agouti coat color gene introduced into its DNA via gene targeting. Its offspring are homozygous for the agouti gene.
Figure 8A. Molecular model for the RecBCD pathway of recombination. This model is based on reactions of DNA and RecBCD with ATP in excess over Mg2+ io
Figure 8A. Molecular model for the RecBCD pathway of recombination. This model is based on reactions of DNA and RecBCD with ATP in excess over Mg2+ ions. Step 1: RecBCD binds to a double-stranded DNA end. Step 2: RecBCD unwinds DNA. RecD is a fast helicase on the 5'-ended strand, and RecB is a slower helicase on the 3'-ended strand (that with an arrowhead) [ref 46 in current Wiki version]. This produces two single-stranded (ss) DNA tails and one ss loop. The loop and tails enlarge as RecBCD moves along the DNA. Step 3: The two tails anneal to produce a second ss DNA loop, and both loops move and grow. Step 4: Upon reaching the Chi hotspot sequence (5' GCTGGTGG 3'; red dot) RecBCD nicks the 3'-ended strand. Further unwinding produces a long 3'-ended ss tail with Chi near its end. Step 5: RecBCD loads RecA protein onto the Chi tail. At some undetermined point, the RecBCD subunits disassemble. Step 6: The RecA-ssDNA complex invades an intact homologous duplex DNA to produce a D-loop, which can be resolved into intact, recombinant DNA in two ways. Step 7: The D-loop is cut and anneals with the gap in the first DNA to produce a Holliday junction. Resolution of the Holliday junction (cutting, swapping of strands, and ligation) at the open arrowheads by some combination of RuvABC and RecG produces two recombinants of reciprocal type. Step 8: The 3' end of the Chi tail primes DNA synthesis, from which a replication fork can be generated. Resolution of the fork at the open arrowheads produces one recombinant (non-reciprocal) DNA, one parental-type DNA, and one DNA fragment.