title: The human 18S U11/U12 snRNP contains a set of novel proteins not found in the U2-dependent spliceosome.
abstract: U11 and U12 snRNPs bind U12-type pre-mRNAs as a preformed di-snRNP complex, simultaneously recognizing the 5' splice site and branchpoint sequence. Thus, within the U12-type prespliceosome, U11/U12 components form a molecular bridge connecting both ends of the intron. We have affinity purified human 18S U11/U12 and 12S U11 snRNPs, and identified their protein components by using mass spectrometry. U11/U12 snRNPs lack all known U1 snRNP proteins but contain seven novel proteins (i.e., 65K, 59K, 48K, 35K, 31K, 25K, 20K) not found in the major spliceosome, four of which (59K, 48K, 35K, and 25K) are U11-associated. Thus, protein-protein and protein-RNA interactions contributing to 5' splice site recognition and/or intron bridging appear to differ significantly in the minor versus major prespliceosome. The majority of U11/U12 proteins are highly conserved in organisms known to contain U12-type introns. However, homologs of those associated with U11 were not detected in Drosophila melanogaster, consistent with the presence of a divergent U11 snRNP in flies. RNAi experiments revealed that several U11/U12 proteins are essential for cell viability, suggesting they play key roles in U12-type splicing. The presence of unique U11/U12 snRNP proteins in the U12-type spliceosome provides insight into potential evolutionary relationships between the major and minor spliceosome.
authors.affiliation: Department of Cellular Biochemistry, Max Planck Institute of Biophysical Chemistry, D-37077 Göttingen, Germany.
authors.forename: Cindy L
authors.initials: CL
authors.lastname: Will
authors.forename: Claudia
authors.initials: C
authors.lastname: Schneider
authors.forename: Markus
authors.initials: M
authors.lastname: Hossbach
authors.forename: Henning
authors.initials: H
authors.lastname: Urlaub
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rauhut
authors.forename: Sayda
authors.initials: S
authors.lastname: Elbashir
authors.forename: Thomas
authors.initials: T
authors.lastname: Tuschl
authors.forename: Reinhard
authors.initials: R
authors.lastname: Lührmann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D012326:RNA Splicing; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000737:chemistry* / Q000235:genetics; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry* / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D017381:Spliceosomes / Q000737:chemistry*
chemical_list: D029721:Drosophila Proteins; D017413:Ribonucleoprotein, U2 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; C098762:U11 small nuclear ribonucleoprotein, human; C552126:U11-U12 small nuclear ribonucleoprotein