Cm. Romfo et al., 3 ' splice site recognition in nematode trans-splicing involves enhancer-dependent recruitment of U2 snRNP, RNA, 7(6), 2001, pp. 785-792
Trans-splicing requires that 5' and 3' splice sites be independently recogn
ized. Here, we have used mutational analyses and a sensitive nuclease prote
ction assay to determine the mechanism of trans-3' splice site recognition
in vitro. Efficient recognition of the 3' splice site is dependent upon bot
h the sequence of the 3' splice site itself and enhancer elements located i
n the 3' exon. We show that the presence of three distinct classes of enhan
cers results in increased binding of U2 snRNP to the branchpoint region. Se
veral lines of evidence strongly suggest that the increased binding of U2 s
nRNP is mediated by USAF. These results expand the roles of enhancers in co
nstitutive splicing and provide direct support for the recruitment model of
enhancer function.