title: Modified nucleotides at the 5' end of human U2 snRNA are required for spliceosomal E-complex formation.
abstract: U2 snRNA, a key player in nuclear pre-mRNA splicing, contains a 5'-terminal m3G cap and many internal modifications. The latter were shown in vertebrates to be generally required for U2 function in splicing, but precisely which residues are essential and their role in snRNP and/or spliceosome assembly is presently not clear. Here, we investigated the roles of individual modified nucleotides of HeLa U2 snRNA in pre-mRNA splicing, using a two-step in vitro reconstitution/complementation assay. We show that the three pseudouridines and five 2'O-methyl groups within the first 20 nucleotides of U2 snRNA, but not the m3G cap, are required for efficient pre-mRNA splicing. Individual pseudouridines were not essential, but had cumulative effects on U2 function. In contrast, four of five 2'O-methylations (at positions 1, 2, 12, and 19) were individually required for splicing. The in vitro assembly of 17S U2 snRNPs was not dependent on the presence of modified U2 residues. However, individual internal modifications were required for the formation of the ATP-independent early spliceosomal E complex. Our data strongly suggest that modifications within the first 20 nucleotides of U2 play an important role in facilitating the interaction of U2 with U1 snRNP and/or other factors within the E complex.
authors.affiliation: Department of Cellular Biochemistry, Max Planck Institute of Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.
authors.forename: Gizem
authors.initials: G
authors.lastname: Dönmez
authors.forename: Klaus
authors.initials: K
authors.lastname: Hartmuth
authors.forename: Reinhard
authors.initials: R
authors.lastname: Lührmann
mesh_terms: D001483:Base Sequence; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008745:Methylation; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011560:Pseudouridine / Q000737:chemistry; D012315:RNA Caps / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing; D012342:RNA, Small Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D012315:RNA Caps; D012342:RNA, Small Nuclear; C405484:U2 small nuclear RNA; D011560:Pseudouridine