Donor and acceptor sites' pictograms. Pictograms of the donor (left) and the acceptor (right) site sequences for the U2 (top) and U12 (bottom) splice sites. The sequence plots for GT-AG and GC-AG U2 introns are given separately. The conserved sequence of the U12 branch point is also shown. From human, mouse, rat, and chicken RefSeq genes, a total number of 337,336, 2506, and 935 splice-site sequences from CDS introns from Ensembl were included in GT-AG, GC-AG, and U12 splice site sets, respectively, to produce the corresponding pictograms.