HollidayJunctions

HollidayJunctions refers to Holliday junctions, the four-stranded DNA structures that form during homologous recombination. These junctions arise when genetic material is exchanged between homologous chromosomes or sister chromatids, typically during the repair of double-strand breaks or during meiosis. The structure is X-shaped, with two strands crossing and pairing with complementary sequences, creating a central crossover point.

Formation and dynamics: Holliday junctions arise after resection creates single-stranded tails that invade homologous DNA. At the crossing point, the strands can migrate along the DNA in a process called branch migration, extending the region of heteroduplex DNA. The junction can be stabilized by various proteins and remains a key intermediate in recombination pathways.

Resolution and outcomes: The junction is eventually cleaved by specialized nucleases in a process known as resolution. Depending on which strands are cut, the outcome can be a crossover, where flanking genetic material is exchanged, or a non-crossover, where only the gene conversion region is altered. In bacteria, resolvases like RuvC perform this function, while eukaryotes employ factors such as GEN1 and MUS81-EME1, often in conjunction with dissolution pathways involving helicases and topoisomerases.

Biological significance and applications: Holliday junctions are central intermediates in genetic recombination, contributing to genetic diversity and error-free DNA repair. They serve as model systems in molecular biology and genetics and have practical applications in DNA nanotechnology, where designed junctions act as dynamic building blocks for constructing nanoscale structures.

History: The concept is named after Robin Holliday, who proposed the four-stranded junction model in 1964.