MUT-15 (also RDE-5; T01C3.8) is a germline protein of the mutator complex with no recognizable domains. MUT-15 is recruited by the B-C region of the Q/N-rich scaffold MUT-16 to perinuclear Mutator foci, and probably binds MUT-16 directly. In turn MUT-15 is needed to bring the NYN-domain proteins NYN-1, NYN-2 and the endoribonuclease RDE-8 into Mutator foci, and for RDE-8 to engage RNAi target mRNA efficiently. Like other mutator-class genes, mut-15 is required for RNAi and for the accumulation of RdRP-dependent secondary 22G siRNAs. It therefore acts as an organizing subunit that links the MUT-16 scaffold to the ribonuclease module of the siRNA amplification machinery.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:1990633 mutator focus | IDA PMID:22713602 MUT-16 promotes formation of perinuclear mutator foci requir... | ACCEPT | Summary: MUT-15 is one of the six mutator proteins observed in perinuclear Mutator foci. Its localization there depends on MUT-16. Reason: Core location, directly observed. It is confirmed by MUT-16-dependent recruitment and by ectopic MUT-16 foci recruiting MUT-15 in muscle cells. Supporting Evidence: PMID:22713602 Here we show that each of the six mutator proteins localizes to punctate foci at the periphery of germline nuclei. PMID:30036386 In brief, MUT-16 is required for localization of MUT-2, MUT-7, RDE-2, MUT-14, and MUT-15, all of which localize independently of one another except for MUT-7, which requires RDE-2 for localization (Fig 1C). |
| GO:0030422 siRNA processing | IMP PMID:30036386 Distinct regions of the intrinsically disordered protein MUT... | NEW | Summary: mut-15 mutants, like other mutator-complex mutants, lose most RdRP-dependent secondary siRNAs. MUT-15 is needed to recruit the RDE-8 and NYN-1/NYN-2 nucleases to Mutator foci and for RDE-8 to engage target mRNA. Reason: MUT-15 does part of the work of secondary siRNA biogenesis as a structural subunit. It places the RDE-8/NYN ribonuclease module in the amplification compartment and is needed for RDE-8 to bind target mRNA, a step upstream of RdRP templating. This is the scaffold case, not only necessity. For the comparator check, the other non-catalytic mutator scaffolds, MUT-16 (IMP) and RDE-2 (IDA), already carry GO:0030422. Supporting Evidence: PMID:30036386 Mutator foci are considered hubs of siRNA amplification because mutations in mut-16 or any of the associated Mutator complex proteins (mut-2, mut-7, mut-14 smut-1, mut-15, rde-2, rde-8, or rrf-1) result in a substantial loss of the RdRP-dependent secondary siRNAs PMID:30036386 Localization of RDE-8 and NYN-1 to Mutator foci requires both mut-16 and mut-15. PMID:25635455 In mut-15(tm1358), mut-16(tm3748), or nyn-1(tm5004); nyn-2(tm4844) mutants, enrichment of sel-1 mRNA by GFP::RDE-8(D76N) RIP was reduced to 22β42% of the WT level (Figure 6B). |
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Download this section (compressed HTML)Q: Does MUT-15 bind RDE-8 and NYN-1/NYN-2 directly, which would make it a protein-macromolecule adaptor between MUT-16 and the ribonuclease module? Or does it act through RNA?
Experiment: Use recombinant pull-downs or yeast two-hybrid tests between MUT-15 fragments and MUT-16 (B-C region), RDE-8, NYN-1 and NYN-2. Then make separation-of-function mut-15 alleles that keep MUT-16 binding but lose RDE-8/NYN recruitment, and measure 22G-RNA levels.
What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The molecular activity of MUT-15 is unknown. It has no recognizable domains, and it has not been shown whether it binds RDE-8, NYN-1 or NYN-2 directly (as an adaptor between them and MUT-16), binds RNA, or has some other activity.
OPEN BIOLOGY MF_DARK
What is known: It is established that MUT-15 localizes to Mutator foci in a MUT-16-dependent way, co-purifies with MUT-16 and RDE-8, and is needed to recruit RDE-8 and NYN-1 to Mutator foci and for secondary siRNA accumulation.
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