Conserved set 1 contains human intronic poly(A) sites whose orthologous sites in mouse or rat genomes were also found to be in introns. Conserved set 2 contains human poly(A) sites that have orthologous sites in mouse or rat genomes, but the orthologous sites were not classified as intronic poly(A) sites due to lack of supporting evidence (for details, see Methods). Nonconserved set contains human intronic poly(A) sites that do not have orthologous sites identified in mouse or rat genomes.

^aAn intronic polyadenylation event is defined as a poly(A) site in a particular intron (5′ss + 3′ss) of a RefSeq or KnownGene mRNA.

^bTerminal exon type is the terminal exon resulting from an intronic polyadenylation event. “Both” indicates that there exist equal numbers of cDNA/EST evidences supporting composite and skipped terminal exons.