 The 2' hydroxyl of the bulged adenosine attacks the 5' splice site, followed by nucleophilic attack on the 3' splice site by the 3' OH of the upstream exon.This results in a branched intron lariat connected by a 2' phosphodiester linkage at the DVI adenosine.Protein machinery is required for splicing "in vivo", and long-range intron-intron and intron-exon interactions are important for splice site positioning, as well as a number of tertiary contacts between motifs, including kissing-loop and tetraloop-receptor interactions.