NCU09880 is a canonical SmG protein that binds snRNA in the heptameric Sm ring. SmG-containing U1, U2, U4 and U5 small nuclear ribonucleoproteins assemble into the spliceosome and support pre-mRNA splicing. SmG also participates in the assembly intermediates that build these RNA-protein particles.
Summary: The SmG-specific domain identifies a canonical Sm-ring subunit.
Reason: The SmG-specific domain identifies a canonical Sm-ring subunit. Characterized yeast SmG participates in the U1, U2, U4 and U5 snRNP scaffolds, and mutational interactions establish its functional contribution to spliceosome assembly and pre-mRNA splicing.
Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal.
Summary: The SmG-specific domain identifies a canonical Sm-ring subunit.
Reason: The SmG-specific domain identifies a canonical Sm-ring subunit. Characterized yeast SmG participates in the U1, U2, U4 and U5 snRNP scaffolds, and mutational interactions establish its functional contribution to spliceosome assembly and pre-mRNA splicing.
Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal.
Summary: The SmG-specific domain identifies a canonical Sm-ring subunit.
Reason: The SmG-specific domain identifies a canonical Sm-ring subunit. Characterized yeast SmG participates in the U1, U2, U4 and U5 snRNP scaffolds, and mutational interactions establish its functional contribution to spliceosome assembly and pre-mRNA splicing.
Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal.
Summary: Canonical SmG contacts the snRNA Sm site within the heptameric ring.
Reason: Canonical SmG contacts the snRNA Sm site within the heptameric ring. Conserved RNA-contact mutagenesis in yeast supports RNA binding by the subunit in its normal complex context.
Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal.
Summary: Canonical SmG contacts the snRNA Sm site within the heptameric ring.
Reason: Canonical SmG contacts the snRNA Sm site within the heptameric ring. Conserved RNA-contact mutagenesis in yeast supports RNA binding by the subunit in its normal complex context.
Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal.
Summary: SmG-containing snRNPs function in nuclear pre-mRNA splicing.
Reason: SmG-containing snRNPs function in nuclear pre-mRNA splicing. The conserved SmG identity and characterized nuclear snRNP membership support nuclear localization; cytoplasmic assembly intermediates are compatible with this annotation.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: Protein-containing complex is correct but uninformative for a canonical SmG subunit.
Reason: Protein-containing complex is correct but uninformative for a canonical SmG subunit. Its supported role is in spliceosomal snRNPs and spliceosome complexes.
Summary: SmG is a substrate subunit in the SMN-mediated Sm assembly intermediate.
Reason: SmG is a substrate subunit in the SMN-mediated Sm assembly intermediate. The human structure explicitly contains SmG in the SmD1/D2/F/E/G pentamer bound to Gemin2 and SMN. The curated ancestral assertion transfers this conserved assembly interaction, not a stable catalytic-spliceosome SMN membership.
Summary: Cap hypermethylation is catalyzed by Tgs1 and is coupled to snRNP biogenesis, so a noncatalytic SmG contribution is plausible.
Reason: Cap hypermethylation is catalyzed by Tgs1 and is coupled to snRNP biogenesis, so a noncatalytic SmG contribution is plausible. The retrieved experiments establish SmG-dependent ring assembly but do not resolve the specific SmG requirement for cap hypermethylation underlying this yeast-to-Neurospora transfer. This is not rejected merely because SmG lacks methyltransferase activity.
Here, we show that yeast Tgs1p, an evolutionarily conserved protein carrying a signature of S-AdoMet methyltransferase, is essential for hypermethylation of the m(7)G caps of both snRNAs and snoRNAs.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
Summary: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog.
Reason: The SmG-specific subfamily distinguishes this protein from the related Lsm7 paralog. Canonical Sm rings scaffold U1, U2, U4 and U5 snRNPs and persist with their snRNAs through the relevant spliceosome intermediates, supporting these conserved memberships and the curator-established phylogenetic assignments.
A seven-subunit Sm protein ring forms a core scaffold of the U1, U2, U4, and U5 snRNPs that direct pre-mRNA splicing.
Core Functions
NCU09880 is a canonical SmG protein that binds snRNA in the heptameric Sm ring. SmG-containing U1, U2, U4 and U5 small nuclear ribonucleoproteins assemble into the spliceosome and support pre-mRNA splicing. SmG also participates in the assembly intermediates that build these RNA-protein particles.
Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal.
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
NCU09880 is a canonical SmG protein that binds snRNA in the heptameric Sm ring. SmG-containing U1, U2, U4 and U5 small nuclear ribonucleoproteins assemble into the spliceosome and support pre-mRNA splicing. SmG also participates in the assembly intermediates that build these RNA-protein particles.
Review rationale: The SmG-specific domain distinguishes this protein from Lsm paralogs. Characterized yeast SmG is part of the canonical RNA-binding ring in U1, U2, U4 and U5 snRNPs. Curator-reviewed GOA includes U2-type prespliceosome (GO:0071004), a cellular-component descendant of spliceosomal complex. The emitted complex term is supported but less precise than that established complex assignment.
Supporting Evidence:
PMID:27417296: "A seven-subunit Sm protein ring forms a core scaffold of the U1, U2, U4, and U5 snRNPs that direct pre-mRNA splicing."
PMID:27417296: "Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal."