The MRX complex is a heterotrimeric

protein complex A protein complex or multiprotein complex is a group of two or more associated polypeptide chains. Protein complexes are distinct from multidomain enzymes, in which multiple active site, catalytic domains are found in a single polypeptide chain. ...

consisting of Mre11,

Rad50 DNA repair protein RAD50, also known as RAD50, is a protein that in humans is encoded by the ''RAD50'' gene. Function The protein encoded by this gene is highly similar to ''Saccharomyces cerevisiae'' Rad50, a protein involved in DNA double- ...

, and Xrs2. It is a budding yeast homolog of the mammalian Mre11-Rad50-Nbs1 (MRN) DNA damage repair complex.

Double-strand break repair

Cells are able to accurately repair DNA double-strand breaks using a process called

homologous recombination 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 (usually DNA as in Cell (biology), cellular organi ...

. By this process DNA sequence information that is lost because of the breakage can be recovered from a second homologous DNA molecule. Homologous recombinational repair is important for removing DNA damage both during

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

and

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

. The repair process begins with the degradation of the 5’ end on either side of the double-strand break to yield 3’ single-stranded DNA tails (a process called end resection). Next the

Rad51 DNA repair protein RAD51 homolog 1 is a protein encoded by the gene ''RAD51''. The enzyme encoded by this gene is a member of the RAD51 protein family which assists in repair of DNA double strand breaks. RAD51 family members are homologous to t ...

protein binds to these tails and initiates a process of strand invasion leading to recovery of genetic information from the undamaged homologous sequence of the second DNA molecule. Studies with the yeast ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'' have shown that end resection is catalyzed by the MRX protein complex. The MRE11 enzyme (one of the three component proteins of the MRX complex) first makes a nick in the DNA at 15 to 20 nucleotides from the 5’ end of the break. This creates an entry point for further processing by exonucleases to complete the initial resection stage of the overall process.

References

Protein complexes {{protein-stub