Figure 1

Generalized homing mechanisms for mobile group I introns and inteins. In both cases, the activity of the endonuclease (which is translated either as a free-standing protein from the intron, or as a fusion with the surrounding intein) leads to a double-strand break in an allele of the host gene that does not contain the intervening sequence. Subsequent repair via homology-driven strand invasion and recombination and DNA replication, using the allele containing the intron or intein (as well as the associated endonuclease coding sequence), completes the homing process. HEG, homing endonuclease gene.