Direct Interactions between Subunits of CPSF and the U2 snRNP Contribute to the Coupling of Pre-mRNA 3′ End Processing and Splicing

Eukaryotic pre-mRNAs are capped at their 5′ ends, polyadenylated at their 3′ ends, and spliced before being exported from the nucleus to the cytoplasm. Although the three processing reactions can be studied separately in vitro, they are coupled in vivo. We identified subunits of the U2 snRNP in highly purified CPSF and showed that the two complexes physically interact. We therefore tested whether this interaction contributes to the coupling of 3′ end processing and splicing. We found that CPSF is necessary for efficient splicing activity in coupled assays and that mutations in the pre-mRNA binding site of the U2 snRNP resulted in impaired splicing and in much reduced cleavage efficiency. Moreover, we showed that efficient cleavage required the presence of the U2 snRNA in coupled assays. We therefore propose that the interaction between CPSF and the U2 snRNP contributes to the coupling of splicing and 3′ end formation.