| We have used expressed sequence tags and cDNAs to identify alternative splicing and single nucleotide polymorphisms in coding regions of human genes, and have created a set of alternative and constitutive splice sites conserved between mouse and human. We show that evolutionarily conserved alternative sites are weaker than constitutive sites, and this difference is not attributable to differences in G+C content or expression level. Detailed analysis of sequence conservation patterns and site scores indicates that evolutionarily conserved alternative splice sites are under selection to maintain their weaker strength. In particular, the high conservation in the region flanking alternatively spliced exons partly reflects splice site sequence conservation. We also identify candidate motifs present in intronic regions adjacent to splice sites that differ significantly in frequency between alternative and constitutive sites. |
