Figure 2.

Splice signal motifs. Sequence motifs for the 5′ss (A), branch site (B), and 3′ss (C) are displayed by using the pictogram program (http://genes.mit.edu/pictogram.html). The height of each letter is proportional to the frequency of the corresponding base at the given position, and bases are listed in descending order of frequency from top to bottom. The RelEnt (in bits) of the motif model used in our analyses (I1M or WMM) relative to the background transcript base composition is also shown. The splice junctions and branch point are marked by inverted triangles.