Other Meganucleases
I-CreI
The I-CreI meganuclease is a protein from the LAGLIDADG family that is found in Chlamydomonas reinhardtii algae. The use of I-CreI is increasing today in genome engineering, structural studies have made it a paradigm for research into homing endonuclease engineering to site direct breaks at natural loci to mediated DNA recombination. I-CreI was the first LAGLIDADG protein to be crystallized with its target DNA.
HO
The HO meganuclease was the first natural meganuclease to be identified. It induces mating-type switching in baker’s yeast.
Baker’s yeast Saccharomyces cerevisiae can be haploid or diploid. Yeast of opposite mating types, “a” and “alpha”, can mate and produce a diploid cell. Diploid cells can sporulate, producing four haploid spores, two spores of mating type “a” and two spores of mating type “alpha”. Wild-type haploid cells can switch mating type at each cell cycle by a finely regulated process of DSB-induced gene conversion. The transcriptionally active MAT locus, which encodes mating type, is cut by the HO meganuclease, and uses one of the two inactive cassettes as a homologous donor template, resulting in a MATa or MATalpha locus.
HO is an atypical LAGLIDADG protein, with a “zinc finger” domain in its COOH-terminal part and very complex transcriptional and post-translational regulation. HO-induced double-strand break (DSB) repair has been widely studied in yeast, and much of our current knowledge of DSB repair is based on this research.
I-TevI
I-TevI is a GIY-YIG protein of phage T4. The biology and biochemistry of I-TevI have been characterized more successfully than those of any other homing endonuclease except I-SceI and HO. Early studies showed that, as with I-SceI and HO, I-TevI was able to promote DSB-induced gene conversion.