Synergistic roles for human U1 snRNA stem-loops in pre-mRNA splicing

During spliceosome assembly, interactions that bring the 5′ and 3′ ends of an intron in proximity are critical for the production of mature mRNA. Here, we report synergistic roles for the stem-loops 3 (SL3) and 4 (SL4) of the human U1 small nuclear RNA (snRNA) in maintaining the optimal U1 snRNP function, and formation of cross-intron contact with the U2 snRNP. We find that SL3 and SL4 bind distinct spliceosomal proteins and combining a U1 snRNA activity assay with siRNA-mediated knockdown, we demonstrate that SL3 and SL4 act through the RNA helicase UAP56 and the U2 protein SF3A1, respectively. In vitro analysis using UV crosslinking and splicing assays indicated that SL3 likely promotes the SL4-SF3A1 interaction leading to enhancement of A complex formation and pre-mRNA splicing. Overall, these results highlight the vital role of the distinct contacts of SL3 and SL4 in bridging the pre-mRNA bound U1 and U2 snRNPs during the early steps of human spliceosome assembly. © 2021 Informa UK Limited, trading as Taylor & Francis Group.National Institute of General Medical Sciences12 month embargo; published online: 09 June 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu