Fig. 5.

Modes of protection against self-cleavage by homing endonucleases. (A) Homing endonuclease gene (HEG) encoded within a group I intron. The intron interrupts the sensitive binding/cleavage site (○). (B) HEG inserted intercistronically, resistance due to sequence differences at the binding/cleavage site (•). (C) HEG inserted intercistronically. Resistance is due to group I intron inserted into sensitive binding/cleavage site. (D) mobA inserted within an ancestral gene 39. Resistance is due to insertion of bypass sequence (Hop) within the sensitive binding/cleavage site. Group I introns, dark bars; homing endonuclease genes, shaded boxes; target genes without insertions, clear boxes; intergenic spaces, thin lines.