Figure 3.

Diversification of splicing endonuclease family and their RNA substrate specificity. (A) Box representation of endA protein unit structure. (B) Comparison of strict (left) and relaxed (right) form of BHB motifs. (C) Possible evolutionary path of endA protein family based on sequence, phylogenetic (Randau et al., 2005c; Tocchini-Valentini et al., 2005b; Fujishima et al., 2011) and molecular studies (Calvin and Li, 2008; Yoshinari et al., 2009; Hirata et al., 2012; Soma et al., 2013). Unit/subunit architecture of five known types [archaeal α₄, α₂, (αβ)₂, ε₂, and eukaryotic αβγδ] and two hypothetical types (korarchaeal α₂ with specific loop, and unknown C. melorae endonuclease) are shown, with colors indicating the phylogenetic relationship.