Group II intron splicing forms
Group II introns share mechanistic ancestry with spliceosomes, forming lariat structure rather than linear product. First step uses internal bulged adenosine within intron domain VI as nucleophile; its 2' OH attacks 5' splice site, generating branched intermediate where intron 5' end linked via 2'-5' phosphodiester to branch point, forming loop. Second step, 5' exon attacks 3' splice site, ligating exons and releasing lariat intron. This lariat pathway underpins evolution of spliceosomal snRNA-mediated splicing in eukaryotic nuclei. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 8, Group II intron lariat formation via branch-point adenosine