A Holliday junction is a branched nucleic acid structure that contains four double-stranded arms joined. These arms may adopt one of several conformations depending on buffer salt concentrations and the sequence of nucleobases closest to the junction. The structure is named after Robin Holliday, the molecular biologist who proposed its existence in 1964. In biology, Holliday junctions are a key intermediate in many types of genetic recombination, as well as in double-strand break repair. These junctions usually have a symmetrical sequence and are thus mobile, meaning that the four individual arms may slide through the junction in a specific pattern that largely preserves base pairing. Additionally, four-arm junctions similar to Holliday junctions appear in some functional RNA molecules. Immobile Holliday junctions, with asymmetrical sequences that lock the strands in a specific position, were artificially created by scientists to study their structure as a model for natural Holliday junctions. These junctions also later found use as basic structural building blocks in DNA nanotechnology, where multiple Holliday junctions can be combined into specific designed geometries that provide molecules with a high degree of structural rigidity. The Holliday junction is a key intermediate in homologous recombination. Many proteins are able to recognize or distort the Holliday junction structure. One such class contains junction-resolving enzymes that cleave the junctions, distorting the structure of the junction in various ways, often pulling the junction into an unstacked conformation, breaking the central base pairs, and changing the angles between the four arms. Here you can see a crystal structure of the Holliday junction-resolving enzyme GEN1 (WT) in complex with product DNA from Thermochaetoides thermophila (PDB code: 5CO8)

#molecularart ... #resolvase ... #holliday ... #xray

Structure rendered with @proteinimaging and depicted with @corelphotopaint