Practice question

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.