Fig. 1.

Homing mechanisms for group I introns (a), inteins (b) and group II introns (c). The homing endonuclease coding sequence of gene A (green) is duplicated in its cognate allele, gene A′. Mobile ORFs and encoded products are green; host gene exons and products are yellow; the other nucleic acid sequence is black, DNA is coloured with a 3D effect and RNA is flat. The ORF position is indicated with a black arrow. HE Homing endonuclease, M maturase, RT reverse-transcriptase, RNP ribonucleoprotein. The different stages of each mechanism are numbered in the scheme. The diagram showing the mechanism of action for group II introns is highly simplified. More detailed figures of their homing mechanisms can be found in specific reviews [158]