In both cases binding occurs on the inner sides of the U, where both Mre11 subunits contribute to holding and manipulating each piece of DNA by means of "recognition loops" in the protein's folded string of amino acid residues. P. furiosus Mre11 has six recognition loops. Mre11 from eukaryotes organisms including yeast, frogs, and humans, whose cells, unlike archaea and bacteria, have membrane-packaged nuclei exhibit only five of these recognition loops but are otherwise similar.
How Mre11 works
The ends of the two DNA helices in the synaptic complex are held in close proximity while one part of each Mre11 protein, called the capping domain, rotates into place to adjust the position of the helices and prepare their ends. Another part of each subunit, called the nuclease domain, accesses individual nucleotides, stripping a strand from one of the helices to leave a so-called 3' tail, essential to the next steps in homologous recombination. The other strand, the 5' tail, is degraded in an Mre11 process known as a "resection," which also depends on nuclease activity.
The branching complex handles the different configuration of a collapsed fork in a different way. Where capping and nuclease domains meet, the twin Mre11s clamp onto the single helix where its division was halted. The 3' strand is held apart and prepared for continuing replication after repair.
Now combining sequencing and biochemical studies of Schizosaccharomyces pombe (fission yeast), by Paul Russell and his lab at Scripps, with models based on images of the P. furiosus Mre11-DNA complexes, the researchers le
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory