Figure 5.

Intein evolution. (A) Models for the coexistence of endonuclease and protein-splicing functions in mobile inteins. (B) Mobile intron and intein evolution. An endonuclease gene is shown invading DNA encoding a self-splicing intron or intein to generate a mobile intron or intein, respectively. The sharing of endonuclease motifs with other proteins to form composite proteins is shown. The formation of a hedgehog protein from an intein is depicted by loss of the C-terminal domain responsible for protein ligation. Symbols are depictions of DNA, with the endonuclease ORF represented by a gray rectangle.