FIGURE 5.

Different modes of recognition of the 3′ splice site in different species. In the yeast, Saccharomyces cerevisiae, introns are AG independent. The splice site is recognized by tight binding of SF1/BBP to the highly conserved branchpoint consensus sequence. In mammals, the site is tripartite; it is identified by weaker binding of SF1/BBP to this site, as well as by binding of the polypyrimidine tract by U2AF⁶⁵ and the YAG by U2AF³⁵. In C. elegans the octamer at the splice site is bound tightly by the U2AF^65/35 complex.