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DNA cleavage

MRX Protein Processes the Cleaved DNA Ends for Assembly of the RecA-like Strand-Exchange Proteins

The DNA at the site of the Spoil-catalyzed double-strand break is processed to generate single-stranded regions needed for assembly of the RecA-like strand-exc.hange proteins. As was observed in the RecBCD pathway from bacteria, this processing generates long segments of single-stranded DNA that terminate in 3' ends (Figure Iff-17), During meiotic recombination, the MRX-enzyme complex is responsible for this DNA processing event. This complex, although not homologous to RecBCD, is also a multi-subunit DNA nuclease. MRX is composed of protein subunits called Mrell, RadSO, and Xrs2; the first letters of these suhunits give the complex its name.

Processing of the DNA at the break site occurs exclusively on the DNA strand that terminates with a 5' end—that is, the strands covalently attached to the Spoil protein (as described above). The strands terminating with 3' ends are not degraded. This DNA-processing reaction is therefore called 5' to 3' resection. The MRX-dependent 5' to 3' resection generates the long ssDNA tails with 3' ends; that are often 1 kb or longer. The MRX complex is also thought to remove the DNA-Iinked Spoil.

Dmc 1 Is a RecA-like Protein that Specifically Functions in Meiotic Recombination

Eukaryotes encode two well-characterized homo lugs of ihe bacterial RecA protein: RadSl and Dmcl. Both proteins function in meiotic


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