What Is a Homing Endonuclease

Homing endonucleases are rare-cutting enzymes that are most often encoded by introns or inteins, but they can also be free-standing, occurring between genes. The genesis of the homing endonuclease field dates back to 1970, with the observation, in genetic crosses between yeast mitochondria, of a significant polarity of recombination for markers of an rRNA gene (Dujon, this Vol.). In 1985, this phenomenon became attributable to an intron-encoded homing endonuclease that initiated recombination within the rRNA gene. Minimally, homing endonucleases are protein enzymes that make a site-specific double-strand break (DSB) at the "homing" site in intron-less or intein-less alleles, thereby initiating a gene conversion event through which the intron or in-tein is copied into the break site (Fig. 2A, B; reviewed by Chevalier and Stoddard 2001; Belfort et al. 2002; Dujon, this Vol.). For the group I and archaeal intron endonucleases and inteins, the recombinogenic ends created at the DSB engage in a strictly DNA-dependent recombination process that duplicates

Fig. 1. Evolution of mobile introns and inteins. Endonuclease genes (red) are proposed to have invaded DNA encoding self-splicing introns or inteins, to generate mobile genetic elements. (Dassa and Pietrokovski, this Vol.)

Back to Basics

0 0

Post a comment