Fig. 8. Model of p14 interactions at the branch site in pre-spliceosomes. The U2 snRNP including U2 snRNA (thick solid line) and its Sm site (black box), and a subset of U2-specific proteins (ellipses) are shown schematically. Exon 2 is depicted by a box, intron sequences by a thin solid line, the polypyrimidine tract by (Py)_n and the branch adenosine (A) and 3′ splice site AG dinucleotide are in bold.