Figure 3

Co-occurring motif pairs are enriched in intronic regions close to splice sites. The BBC-COOC algorithm was used to search for significantly co-occurring motif pairs in symmetrically placed 50-nucleotide regions located at increasing distances from exon boundaries. The numbers of such pairs falls off sharply beyond 100 nucleotides and are reduced to background levels beyond 200 nucleotides. (a) Co-occurring motif pairs around constitutive exons. (b) Co-occurring motif pairs around alternative exons.