FIGURE 1.

Consensus sequences of human U12- and U2-type introns. The height of the letters in each position indicates the relative frequency of individual nucleotides in that position. For frequency calculation the U12-type splice site sequences were obtained from U12DB,⁷ and the corresponding 5′ss and 3′ss frequencies for U2-type introns from the Splice Rack database (Ref ⁸; http://katahdin.mssm.edu/splice/index.cgi?database=spliceNew2) and the branch point sequences (BPS) data from Gao et al.,⁹ The sequence logos were generated using the enoLOGOS web server.¹⁰