NCU09880 encodes Neurospora crassa small nuclear ribonucleoprotein G (SmG), an 85-residue Sm-fold protein. With SmE and SmF it forms the F-E-G subcomplex that joins the D1-D2 and D3-B subcomplexes to build the heptameric Sm ring on the uridine-rich Sm site of the U1, U2, U4 and U5 snRNAs, where SmG contacts one nucleobase through a conserved Arg/Phe/Asn triad. The Sm ring is the core scaffold of these spliceosomal snRNPs, so SmG travels with them into the U4/U6.U5 tri-snRNP and the successive spliceosome assemblies that carry out nuclear pre-mRNA splicing. Before ring closure, Sm subunits pass through an SMN-Gemin2-dependent assembly intermediate.
Summary: SmG is a structural subunit of the Sm core that is assembled onto snRNA to build spliceosomal snRNPs.
Reason: NCU09880 is a full-length canonical SmG (PANTHER PTHR10553:SF2, shared with characterised yeast SmG). Sm subunits pre-form the F-E-G subcomplex and then assemble with the other subcomplexes onto the snRNA Sm site; as a subunit of the assembled core, SmG contributes structure to this assembly process rather than merely being required for it. Accepted as a core process.
Summary: SmG-containing Sm rings scaffold the snRNPs that carry out pre-mRNA splicing.
Reason: The PAINT node PTN000058285 groups NCU09880 with experimentally characterised fungal and animal SmG; the IEA rows agree. Yeast SmG RNA-contact mutations are lethal in combination with mutations in other Sm subunits, showing the subunit contributes to the essential splicing function of the ring. Core process.
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 Sm rings scaffold the snRNPs that carry out pre-mRNA splicing.
Reason: The PAINT node PTN000058285 groups NCU09880 with experimentally characterised fungal and animal SmG; the IEA rows agree. Yeast SmG RNA-contact mutations are lethal in combination with mutations in other Sm subunits, showing the subunit contributes to the essential splicing function of the ring. Core process.
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 contacts a nucleobase of the snRNA Sm site within the heptameric ring; the contact residues are conserved in NCU09880.
Reason: In the Sm ring each subunit engages one nucleobase of the U-rich Sm site through a conserved Arg/aromatic/Asn triad; SmG is one of the seven contacting subunits. The triad residues and the SmE-bridging Arg are conserved in NCU09880. The IBA contributes_to qualifier (RNA binding by the ring as a whole) is the most accurate reading; the IEA enables row asserts the same function and is consistent with it. RNA binding is as specific as warranted, since GO has no Sm-site-specific snRNA-binding term that would apply to all four snRNAs.
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 contacts a nucleobase of the snRNA Sm site within the heptameric ring; the contact residues are conserved in NCU09880.
Reason: In the Sm ring each subunit engages one nucleobase of the U-rich Sm site through a conserved Arg/aromatic/Asn triad; SmG is one of the seven contacting subunits. The triad residues and the SmE-bridging Arg are conserved in NCU09880. The IBA contributes_to qualifier (RNA binding by the ring as a whole) is the most accurate reading; the IEA enables row asserts the same function and is consistent with it. RNA binding is as specific as warranted, since GO has no Sm-site-specific snRNA-binding term that would apply to all four snRNAs.
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: Mature SmG-containing snRNPs act in nuclear pre-mRNA splicing.
Reason: Nuclear localization follows from membership of the splicing snRNPs; there is no Neurospora localization experiment, but the inference is evolutionarily grounded in subfamily membership. A cytoplasmic assembly phase is likely in this lineage but does not contradict nuclear residence of the functional particle.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as characterised yeast SmG, so the Sm-ring membership in spliceosomal snRNPs is evolutionarily grounded.
Reason: The SmG-specific InterPro signature (IPR034098) and PANTHER subfamily SF2 place NCU09880 with experimentally characterised budding- and fission-yeast SmG, not with the Lsm7 paralog. Canonical Sm rings scaffold the U1, U2, U4 and U5 snRNPs, which form the spliceosome, so spliceosomal complex is correct and is the appropriate general component term for this subunit.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: Protein-containing complex is correct but uninformative for a canonical SmG subunit.
Reason: This ARBA-derived term is true but far less specific than the supported memberships. The informative replacement is spliceosomal complex (GO:0005681), which the gene already carries (IEA, accepted) and which subsumes the snRNP-level memberships also accepted here.
Summary: SmG is a substrate subunit of the SMN-Gemin2-Sm assembly intermediate; Neurospora encodes candidate SMN and Gemin2 homologs.
Reason: The PAINT node PTN000058285, which contains NCU09880, carries the SMN-Sm protein complex assertion seeded from human SNRPG, whose SmD1/D2/F/E/G pentamer was crystallised bound to Gemin2 and the SMN Gemin2-binding domain. Neurospora is not obviously outside the clade that retained this machinery: it encodes a protein with the SMN Gemin2-binding domain (NCU01700) and a SIP1/Gemin2-family protein (NCU00620), although neither has been studied. The complex is a transient assembly intermediate in which SmG is a client, so the annotation is retained but not as a core function (the functional snRNP memberships are core).
Neurospora crassa encodes one protein with the SMN Gemin2-binding domain (NCU01700, Q7RY22) and one SIP1-family (Gemin2/Brr1) protein (NCU00620, Q7SI32)
Summary: Cap hypermethylation is catalysed by Tgs1; the yeast experiment behind this transfer depleted SmE, not SmG, and PAINT did not propagate the term.
Reason: This Ensembl Compara row transfers a yeast SmG annotation that rests on PMID:9528767, where depletion of SmE (and, cited there, SmD1/SmD3) reduced snRNA TMG-cap formation; SmG itself was not assayed for hypermethylation. The result shows that Sm-core assembly on the Sm site is a prerequisite for Tgs1-catalysed hypermethylation, i.e. the snRNP is the substrate-bearing particle and Tgs1 performs the methylation. That is necessity rather than participation by SmG, and PAINT curators, who propagated the snRNP and splicing terms from the same SmG node, did not propagate this one. Not rejected outright because the Sm ring is the platform recognised by the methylase, but it is an over-annotation for SmG.
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: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Summary: NCU09880 is a full-length SmG in the same PANTHER subfamily (PTHR10553:SF2) as the characterised yeast SmG proteins, so canonical Sm-ring membership of this snRNP-containing complex is evolutionarily grounded.
Reason: PANTHER subfamily SF2 and the SmG-specific signature place NCU09880 with experimentally characterised budding- and fission-yeast SmG rather than with Lsm7. The Sm ring is the core scaffold of the U1, U2, U4 and U5 snRNPs and remains bound to these snRNAs as they pass through the tri-snRNP, prespliceosome, spliceosome and intron-lariat stages; the PAINT node placement (or Compara ortholog transfer from yeast experimental data) is consistent with this. No Neurospora-specific divergence is apparent: the snRNA-contact residues are conserved.
Q7S234 shares PANTHER subfamily PTHR10553:SF2 with budding-yeast SMX2 (P40204), fission-yeast smg1 (O74966) and Drosophila SNRPG (Q9VXE0)
Core Functions
Subunit of the heptameric Sm ring that binds the snRNA Sm site and forms the core scaffold of the U1, U2, U4 and U5 spliceosomal snRNPs, thereby contributing to snRNP assembly and nuclear 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.
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 InterPro signature (IPR034098) places this protein with characterized yeast SmG rather than the Lsm7 paralog, and yeast SmG is a subunit of the Sm ring that forms the core of the U1, U2, U4 and U5 snRNPs. Spliceosomal complex is correct, but the gene already carries exactly this term in GOA (InterPro2GO IEA, accepted in the gene review), together with more specific accepted complex terms such as U2-type prespliceosome (GO:0071004), so the prediction is not novel.
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."