Crossover junction endonuclease MUS81 is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that in humans is encoded by the ''MUS81''

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 ...

. In mammalian somatic cells, MUS81 and another structure specific DNA endonuclease, XPF (

ERCC4 ERCC4 is a protein designated as DNA repair endonuclease XPF that in humans is encoded by the ''ERCC4'' gene. Together with ERCC1, ERCC4 forms the ERCC1-XPF enzyme complex that participates in DNA repair and DNA recombination. The nuclease enz ...

), play overlapping and essential roles in completion of homologous recombination. The significant overlap in function between these enzymes is most likely related to processing joint molecules such as

D-loop In molecular biology, a displacement loop or D-loop is a DNA structure where the two strands of a double-stranded DNA molecule are separated for a stretch and held apart by a third strand of DNA. An R-loop is similar to a D-loop, but in this ca ...

s and nicked Holliday junctions.

Meiosis

MUS81 is a component of a minor chromosomal crossover (CO) pathway in the

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 r ...

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

, plants and vertebrates. However, in the protozoan ''

Tetrahymena ''Tetrahymena'', a unicellular eukaryote, is a genus of free-living ciliates. The genus Tetrahymena is the most widely studied member of its phylum. It can produce, store and react with different types of hormones. Tetrahymena cells can recog ...

thermophila'', MUS81 appears to be part of an essential (if not the predominant) CO pathway. The MUS81 pathway also appears to be the predominant CO pathway in the fission yeast ''

Schizosaccharomyces pombe ''Schizosaccharomyces pombe'', also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically measur ...

''.

The relationship of the CO pathway to the overall process of meiotic recombination is illustrated in the accompanying diagram. Recombination during

is often initiated by a DNA double-strand break (DSB). During recombination, sections of DNA at the 5' ends of the break are cut away in a process called ''resection''. In the ''strand invasion'' step that follows, an overhanging 3' end of the broken DNA molecule "invades" the DNA of an homologous chromosome that is not broken forming a displacement loop (

). After strand invasion, the further sequence of events may follow either of two main pathways, leading to a crossover (CO) or a non-crossover (NCO) recombinant (see Genetic recombination). The pathway leading to a CO involves a double Holliday junction (DHJ) intermediate. Holliday junctions need to be resolved for CO recombination to be completed. MUS81-MMS4, in the budding yeast ''

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

'', is a DNA structure-selective endonuclease that cleaves joint DNA molecules formed during

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 cellular organisms but may ...

and mitosis. The MUS81-MMS4 endonuclease, although a minor resolvase for CO formation in ''S. cerevisiae'', is crucial for limiting chromosome entanglements by suppressing multiple consecutive recombination events from initiating from the same DSB. Mus81 deficient mice have significant meiotic defects including the failure to repair a subset of DSBs.

Interactions

MUS81 has been shown to

interact Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...

with CHEK2.

Meiosis

Interactions

References

Further reading