FIG. 1.

Distribution of branch site-to-3′ splice site distances in putative U12-dependent introns. The data are from the compilation of putative U12-dependent introns in Burge et al. (5). The solid line shows the distribution for all introns, while the black and grey bars show the distribution of distances in the AU-AC and GU-AG subclasses of U12-dependent introns, respectively. The branch site is assumed to be the position of the second adenosine in the branch site consensus sequence UCCUUAAC. All branch sites could be aligned with the consensus without ambiguity. In a few cases, the presumed branch site was a G residue.