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RecBCD, also known as Exonuclease V, is a protein of the E. coli bacterium that initiates recombinational repair from DNA double strand breaks which are a common result of ionizing radiation, replication errors, endonucleases, oxidative damage and a host of other factors. It is both a helicase that unwinds, or separates the strands of, DNA and a nuclease that makes single-stranded nicks in DNA.
Additional recommended knowledge
RecBCD is composed of three different subunits, encoded by the recB, recC, and recD genes. Both the RecB and RecD subunits are helicases, i.e. energy-dependent molecular motors that unwind DNA or RNA.
RecBCD is unusual amongst helicases in that it recognizes a specific sequence in DNA, 5'-GCTGGTGG-3', that is known as Chi. After it initiates unwinding, RecBCD makes nicks on the strand that contains the unwound 3' end. When RecBCD encounters a Chi site on this strand as it is unwinding DNA, it makes a final nick and pauses. It has been proposed that this pause is a consequence of a conformational rearrangement in the protein that changes its properties. When RecBCD resumes unwinding, it now nicks the opposite strand (i.e. that containing the 5' unwound end). As a consequence, the 3' strand remains intact downstream of Chi. This is important because the strand exchange protein, RecA, that is responsible for the next step of recombinational repair needs a single-strand molecule with a 3' end.
RecBCD is also a model enzyme for the use of single molecule fluorescence as an experimental technique used to better understand the function of protein-DNA interactions.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "RecBCD". A list of authors is available in Wikipedia.|