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Meiotic recombination protein DMC1/LIM15 homolog is a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
that in humans is encoded by the ''DMC1''
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
. Meiotic recombination protein Dmc1 is a homolog of the bacterial strand exchange protein RecA. Dmc1 plays the central role in homologous recombination in meiosis by assembling at the sites of programmed DNA double strand breaks and carrying out a search for allelic DNA sequences located on homologous chromatids. The name "Dmc" stands for "disrupted meiotic cDNA" and refers to the method used for its discovery which involved using clones from a meiosis-specific cDNA library to direct knock-out mutations of abundantly expressed meiotic genes. The Dmc1 protein is one of two homologs of RecA found in eukaryotic cells, the other being Rad51. In budding yeast, Rad51 serves as a strand exchange protein in mitosis where it is critical for the repair of DNA breaks. Rad51 is converted to an accessory factor for Dmc1 during meiosis by inhibition of its strand exchange activity. Homologs of DMC1 have been identified in many organisms including divergent fungi, plants and mammals including humans.


Discovery

The DMC1 gene and protein were discovered in the budding yeast S. cerevisiae by
Douglas Bishop Douglas may refer to: People * Douglas (given name) * Douglas (surname) Animals *Douglas (parrot), macaw that starred as the parrot ''Rosalinda'' in Pippi Longstocking * Douglas the camel, a camel in the Confederate Army in the American Civil ...
when he was a postdoctoral fellow in the laboratory of
Nancy Kleckner Nancy Kleckner is the Herchel Smith Professor of Molecular Biology at Harvard University and principal investigator at the Kleckner Laboratory at Harvard University. Education Nancy Kleckner worked with Matt Meselson as an undergraduate at ...
at Harvard University.


Function

The protein encoded by this gene is essential for meiotic homologous recombination. Genetic recombination in meiosis plays an important role in generating diversity of genetic information and facilitates the reductional segregation of chromosomes that must occur for formation of gametes during sexual reproduction. Like other members of the Rad51/RecA family, Dmc1 stabilizes strand exchange intermediates (Rad1/RecA-stretched DNA, or RS-DNA) in stretched triplets similar to B form DNA. Each molecule of the protein binds a triplet of nucleotides, and the strength of that binding, as assessed by the change in
Gibbs free energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature an ...
, can be assessed by the length of time that a labelled dsDNA probe with a short homologous sequence remains bound to a DNA containing a short region of homology to it. A study of this type has shown that a mismatch in any of the three positions at the end of a stretch of homology will not increase the length of time that the probe remains bound, and in Rad51 or RecA constructs an internal mismatch will cause a similar reduction in binding time. All of the enzymes are capable of "stepping over" a mismatch and continuing to bind the probe more firmly if a longer region of homology exists. However, with Dmc1 a triplet with a single internal (but not terminal) mismatch will contribute to the stability of probe binding to a similar extent as one without a mismatch. In this way, Dmc1 is specially suited to its role as a meiosis-specific recombinase, as this activity permits it more effectively to catalyze recombination between sequences that are not perfectly matched.


Interactions

DMC1 (gene) has been shown to
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with
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 th ...
. The protein has also been shown to bind Tid1(Rdh54), Mei5/Sae3, and Hop2/Mnd1. All of these interacting proteins act to enhance Dmc1's activity in purified systems and are also implicated as being required for Dmc1 function in cells.


Rad51 interaction with Dmc1

During
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...
, the two
recombinases Recombinases are genetic recombination enzymes. Site specific recombinases DNA recombinases are widely used in multicellular organisms to manipulate the structure of genomes, and to control gene expression. These enzymes, derived from bacteri ...
,
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 th ...
and Dmc1, interact with single-stranded DNA to form specialized filaments that are adapted for facilitating recombination between homologous chromosomes. Both Dmc1 and Rad51 have an intrinsic ability to self-aggregate. The presence of Rad51 filaments stabilizes adjacent Dmc1 filaments and conversely Dmc1 stabilizes adjacent Rad51 filaments. A model was proposed in which Dmc1 and Rad51 form separate filaments on the same single stranded DNA and cross-talk between the two recombinases affects their biochemical properties. During meiosis, even in the absence of Rad51 strand exchange activity, Dmc1 appears to be able to repair all meiotic DNA breaks, and this absence does not affect meiotic crossing over rates.


References


Further reading

* * * * * * * * * * * * {{PDB Gallery, geneid=11144 Genes on human chromosome 22