Holliday junction

The Holliday junction structure (so called holliday junction) is an important intermediate step of crossing- overs. It helps in the exchange of genetic information between two homologous ( similar or identical ) and non- homologous DNA strands. The process is catalyzed by the enzyme recombinase. It has four sub-units, which bind to one of the two DNA helices. The result is a Rekombinationssynapse.

The DNA exchange begins with the splitting of a single strand of each helix. Now the free 5' - hydroxyl groups each bind to a tyrosine residue of the subunit and are transported to the other side. There they bind to the 3'- phosphate group of the other double strand. Now this is called a Holliday junction. There is an exchange of DNA by rotating both strands. The single strands will now be transferred to the other helix.

Is the exchange of a few nucleotides 1000 completed, is re- catalyzed cleavage takes place and the two helices are separated from one another.

The Holliday junction is named after the Australian researcher Robin Holliday, who drafted the prototypical model of general recombination in 1964.