SMN-assisted assembly of snRNP-specific Sm cores in trypanosomes.
Spliceosomal small nuclear ribonucleoproteins (snRNPs) in trypanosomes contain either the canonical heptameric Sm ring (U1, U5, spliced leader snRNPs), or variant Sm cores with snRNA-specific Sm subunits (U2, U4 snRNPs). Searching for specificity factors, we identified SMN and Gemin2 proteins that are highly divergent from known orthologs. SMN is splicing-essential in trypanosomes and nuclear-localized, suggesting that Sm core assembly in trypanosomes is nuclear. We demonstrate in vitro that SMN is sufficient to confer specificity of canonical Sm core assembly and to discriminate against binding to nonspecific RNA and to U2 and U4 snRNAs. SMN interacts transiently with the SmD3B subcomplex, contacting specifically SmB. SMN remains associated throughout the assembly of the Sm heteroheptamer and dissociates only when a functional Sm site is incorporated. These data establish a novel role of SMN, mediating snRNP specificity in Sm core assembly, and yield new biochemical insight into the mechanism of SMN activity.
Palfi
Zsofia
Z
Institute of Biochemistry, Justus Liebig University of Giessen, Giessen, Germany.
Jaé
Nicolas
N
Preusser
Christian
C
Kaminska
Katarzyna H
KH
Bujnicki
Janusz M
JM
Lee
Ju Huck
JH
Günzl
Arthur
A
Kambach
Christian
C
Urlaub
Henning
H
Bindereif
Albrecht
A
D000595:Amino Acid Sequence; D000818:Animals; D018832:Molecular Chaperones / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry / Q000378:metabolism; D055532:SMN Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D017381:Spliceosomes / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000378:metabolism*; D055517:snRNP Core Proteins / Q000737:chemistry / Q000378:metabolism*
D018832:Molecular Chaperones; D009687:Nuclear Proteins; D017411:Ribonucleoproteins, Small Nuclear; D055532:SMN Complex Proteins; D055517:snRNP Core Proteins