Introduction to Genetic Analysis 474

Introduction to - 44200_14_p451-480 1:09 PM Page 473 14.4 The mechanism of meiotic crossing-over 473 Double-strand break Sister chromatids

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HOMOLOGOUS RECOMBINATION The mechanism of homologous recombination utilizes the sister chromatid to repair double-strand breaks. For this reason, repair is usually error-free. The mechanism of homologous re- combination is shown in Figure 14-33. Key steps are the binding of the broken ends by specialized proteins and enzymes, the trimming of the 5 9 ends to expose single- stranded regions, and the coating of these regions with proteins that include the RecA homolog, RAD51. Recall that during the SOS response, RecA monomers associate with regions of single-stranded DNA to form long heli- cal ±laments. Similarly, RAD51 forms long ±laments as it associates with the exposed single-stranded region. The RAD51–DNA ±lament then takes part in a re- markable search of the undamaged sister chromatid for the complementary sequence that will be used as a tem- plate for DNA synthesis. Once the complementary re- gion is found, a joint molecule forms between homolo- gous damaged and undamaged duplex DNAs. The
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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