title: Interaction between the RNA binding domains of Ser-Arg splicing factor 1 and U1-70K snRNP protein determines early spliceosome assembly.
abstract: It has been widely accepted that the early spliceosome assembly begins with U1 small nuclear ribonucleoprotein (U1 snRNP) binding to the 5' splice site (5'SS), which is assisted by the Ser/Arg (SR)-rich proteins in mammalian cells. In this process, the RS domain of SR proteins is thought to directly interact with the RS motif of U1-70K, which is subject to regulation by RS domain phosphorylation. Here we report that the early spliceosome assembly event is mediated by the RNA recognition domains (RRM) of serine/arginine-rich splicing factor 1 (SRSF1), which bridges the RRM of U1-70K to pre-mRNA by using the surface opposite to the RNA binding site. Specific mutation in the RRM of SRSF1 that disrupted the RRM-RRM interaction also inhibits the formation of spliceosomal E complex and splicing. We further demonstrate that the hypo-phosphorylated RS domain of SRSF1 interacts with its own RRM, thus competing with U1-70K binding, whereas the hyper-phosphorylated RS domain permits the formation of a ternary complex containing ESE, an SR protein, and U1 snRNP. Therefore, phosphorylation of the RS domain in SRSF1 appears to induce a key molecular switch from intra- to intermolecular interactions, suggesting a plausible mechanism for the documented requirement for the phosphorylation/dephosphorylation cycle during pre-mRNA splicing.
authors.affiliation: Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, CA 92093, USA.
authors.forename: Suhyung
authors.initials: S
authors.lastname: Cho
authors.forename: Amy
authors.initials: A
authors.lastname: Hoang
authors.forename: Rahul
authors.initials: R
authors.lastname: Sinha
authors.forename: Xiang-Yang
authors.initials: XY
authors.lastname: Zhong
authors.forename: Xiang-Dong
authors.initials: XD
authors.lastname: Fu
authors.forename: Adrian R
authors.initials: AR
authors.lastname: Krainer
authors.forename: Gourisankar
authors.initials: G
authors.lastname: Ghosh
mesh_terms: D001665:Binding Sites; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D012322:RNA Precursors / Q000378:metabolism; D012326:RNA Splicing; D016601:RNA-Binding Proteins / Q000378:metabolism*; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism*; D000068103:Serine-Arginine Splicing Factors; D017381:Spliceosomes / Q000378:metabolism*
chemical_list: D009687:Nuclear Proteins; D012322:RNA Precursors; D016601:RNA-Binding Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; C490687:Snrnp70 protein, mouse; D000068103:Serine-Arginine Splicing Factors