Homing endonuclease

Homing endonucleases can thereby transmit their genes horizontally within a host population, increasing their allele frequency at greater than Mendelian rates.

Although the origin and function of homing endonucleases is still being researched, the most established hypothesis considers them as selfish genetic elements,[1] similar to transposons, because they facilitate the perpetuation of the genetic elements that encode them independent of providing a functional attribute to the host organism.

Homing endonuclease recognition sequences are long enough to occur randomly only with a very low probability (approximately once every 7×109 bp),[2] and are normally found in one or very few instances per genome.

Once the enzyme is synthesized, it breaks the chromosome in the HEG− allele, initiating a response from the cellular DNA repair system.

The damage is repaired using recombination, taking the pattern of the opposite, undamaged DNA allele, HEG+, that contains the gene for the endonuclease.

Crystal structure of I-CreI bound to its DNA recognition sequence . The enzyme binds as a homodimer; one subunit is depicted in yellow, the other in pink. The enzyme is shown in surface representation; DNA molecule is shown as a collection of spheres, each colored according to its chemical element .