Evolution
We have proposed an overall model for the evolution of group II introns, which we have termed the “Retroelement Ancestor Hypothesis”. This hypothesis predicts that the basic structural forms of group II intron ribozymes differentiated as components of retroelements in bacteria, with the most primitive group II introns having somewhat unusual and hybrid features. The “standard” IIA and IIB structures are proposed to have evolved in the mitochondrial and chloroplast-like lineages of introns, and the many ORF-less introns in organelles are predicted to be derived by ORF loss. (see
Toor et al. for details). It is important to note that the hypothesis does not address the ultimate origin of the ribozymes, i.e., whether the ribozymes are descendants of the RNA World.
