MUT-16 is a glutamine/asparagine (Q/N)-rich scaffold protein essential for the formation of Mutator foci, perinuclear phase-separated condensates that serve as sites for siRNA amplification in the C. elegans germline. MUT-16 nucleates the assembly of the mutator complex, recruiting RNA-dependent RNA polymerase RRF-1 and other mutator proteins to form a specialized RNA processing compartment. Through its scaffold function, MUT-16 is required for RNA interference (RNAi) and the silencing of more than 2,000 endogenous genes, including transposable elements. Mutator foci are adjacent to, but distinct from, P granules, and both represent key germline RNA regulatory compartments.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:1990633 mutator focus | IDA PMID:22713602 MUT-16 promotes formation of perinuclear mutator foci requir... | ACCEPT | Summary: MUT-16 localizes to punctate foci at the periphery of germline nuclei, termed Mutator foci (PMID:22713602). This is the defining paper that characterized Mutator foci as a distinct subcellular compartment. MUT-16 is not merely a component but is specifically required for the formation of Mutator foci - in its absence, these foci fail to form. Reason: This is a core annotation supported by direct experimental evidence. PMID:22713602 demonstrates that MUT-16 localizes to Mutator foci using fluorescent protein tagging and microscopy. The paper establishes that MUT-16 is essential for Mutator foci formation, making this localization annotation highly accurate. Supporting Evidence: PMID:22713602 Here we show that each of the six mutator proteins localizes to punctate foci at the periphery of germline nuclei. The Mutator foci are adjacent to P granules but are not dependent on core P-granule components or other RNAi pathway factors for their formation or stability. PMID:22713602 The glutamine/asparagine (Q/N)-rich protein MUT-16 is specifically required for the formation of a protein complex containing the mutator proteins, and in its absence, Mutator foci fail to form at the nuclear periphery. file:worm/mut-16/mut-16-deep-research-falcon.md MUT-16 foci are **adjacent to P granules** (e.g., PGL-1-marked), consistent with spatially coupled but compositionally distinct nuage subcompartments. |
| GO:1990633 mutator focus | IDA PMID:24684932 MUT-14 and SMUT-1 DEAD box RNA helicases have overlapping ro... | ACCEPT | Summary: PMID:24684932 confirms MUT-16 localization to Mutator foci and its role in nucleating the mutator complex. The study demonstrates that MUT-16 is the scaffold for the mutator complex that silences more than 2,000 C. elegans genes. Reason: This annotation is well-supported. PMID:24684932 provides additional evidence for MUT-16 localization to Mutator foci while investigating the roles of MUT-14 and SMUT-1 DEAD box helicases that function in this compartment. Supporting Evidence: PMID:24684932 More than 2,000 C. elegans genes are targeted for RNA silencing by the mutator complex, a specialized small interfering RNA (siRNA) amplification module which is nucleated by the Q/N-rich protein MUT-16. PMID:24684932 The mutator complex localizes to Mutator foci adjacent to P granules at the nuclear periphery in germ cells. |
| GO:1990633 mutator focus | IDA PMID:32338603 A tudor domain protein, SIMR-1, promotes siRNA production at... | ACCEPT | Summary: PMID:32338603 further characterizes Mutator foci as phase-separated condensates and confirms MUT-16 localization. This study identifies SIMR-1 foci as distinct from but adjacent to both P granules and Mutator foci. Reason: Provides additional confirmation of MUT-16 localization to Mutator foci and adds the important characterization that these are phase-separated condensates, consistent with MUT-16's Q/N-rich intrinsically disordered regions. Supporting Evidence: PMID:32338603 SIMR-1 also localizes to distinct subcellular foci adjacent to P granules and Mutator foci, two phase-separated condensates that are the sites of piRNA-dependent mRNA recognition and mutator complex-dependent siRNA amplification, respectively. file:worm/mut-16/mut-16-deep-research-falcon.md Mutator foci display multiple properties consistent with **liquid–liquid phase separation**: spherical morphology, sensitivity to 1,6-hexanediol, temperature sensitivity, concentration-threshold behavior, and rapid partial FRAP recovery. |
| GO:0003674 molecular_function | ND GO_REF:0000015 | MODIFY | Summary: This is a placeholder annotation indicating no specific molecular function has been assigned. However, based on current literature, MUT-16 functions as a molecular condensate scaffold that nucleates assembly of the mutator complex. Reason: MUT-16 has a well-characterized molecular function as a scaffold protein that brings together components of the mutator complex through its Q/N-rich intrinsically disordered regions, promoting phase separation and complex assembly. This function is analogous to molecular condensate scaffold activity. Proposed replacements: molecular condensate scaffold activity Supporting Evidence: PMID:22713602 The glutamine/asparagine (Q/N)-rich protein MUT-16 is specifically required for the formation of a protein complex containing the mutator proteins, and in its absence, Mutator foci fail to form at the nuclear periphery. PMID:24684932 More than 2,000 C. elegans genes are targeted for RNA silencing by the mutator complex, a specialized small interfering RNA (siRNA) amplification module which is nucleated by the Q/N-rich protein MUT-16. file:worm/mut-16/mut-16-deep-research-falcon.md MUT-16 is **not an enzyme** with a defined catalytic reaction; instead, its primary function is **structural/organizational** file:worm/mut-16/mut-16-deep-research-falcon.md a **C-terminal region (JKL; aa ~773–1050)** is sufficient for foci formation and is ~70% disordered; it is necessary and sufficient for Mutator-foci assembly. |
| GO:0030422 siRNA processing | IMP PMID:22713602 MUT-16 promotes formation of perinuclear mutator foci requir... | ACCEPT | Summary: MUT-16 is required for siRNA amplification. Genes with high siRNA levels (indicative of multiple amplification rounds) are disproportionally affected in mut-16 mutants. RdRP RRF-1 colocalizes with MUT-16 at Mutator foci. Reason: The GO term siRNA processing includes siRNA amplification by RNA-dependent RNA polymerase according to the term definition. PMID:22713602 provides strong evidence that MUT-16 is required for this process, with mutants showing disproportionate effects on genes requiring siRNA amplification. Supporting Evidence: PMID:22713602 The RdRP RRF-1 colocalizes with MUT-16 at Mutator foci, suggesting a role for Mutator foci in siRNA amplification. PMID:22713602 Furthermore, we demonstrate that genes that yield high levels of siRNAs, indicative of multiple rounds of siRNA amplification, are disproportionally affected in mut-16 mutants compared with genes that yield low levels of siRNAs. PMID:22713602 We propose that the mutator proteins and RRF-1 constitute an RNA processing compartment required for siRNA amplification and RNA silencing. file:worm/mut-16/mut-16-deep-research-falcon.md One study baseline reports that **~2,300 mutator-target genes** showed **>3-fold depletion** of mutator-dependent 22G-RNAs in **mut-16**. |
| GO:0005634 nucleus | IDA PMID:12906791 A genome-wide screen identifies 27 genes involved in transpo... | MODIFY | Summary: PMID:12906791 was an early genome-wide screen that identified mut-16 as required for transposon silencing. The nuclear localization annotation may be imprecise - Mutator foci are actually in the perinuclear cytoplasm, adjacent to the nuclear envelope, not within the nucleus. Reason: Later studies (PMID:22713602) clearly established that MUT-16 localizes to perinuclear Mutator foci in the germline cytoplasm, adjacent to P granules. These foci are at the nuclear periphery but in the cytoplasm, not inside the nucleus. The more precise annotation is to mutator focus (GO:1990633). Proposed replacements: mutator focus 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:22713602 The Mutator foci are adjacent to P granules but are not dependent on core P-granule components or other RNAi pathway factors for their formation or stability. file:worm/mut-16/mut-16-deep-research-falcon.md MUT-16 localizes to **punctate perinuclear foci** throughout the germline. |
| GO:0005737 cytoplasm | IDA PMID:12906791 A genome-wide screen identifies 27 genes involved in transpo... | KEEP AS NON CORE | Summary: MUT-16 is indeed cytoplasmic, specifically in perinuclear Mutator foci. While technically correct, this annotation is too general given the specific localization to Mutator foci that is now well-established. Reason: The cytoplasm annotation is technically correct since Mutator foci are cytoplasmic structures at the nuclear periphery. However, it is less informative than the mutator focus annotation (GO:1990633) which captures the specific subcellular localization. Supporting Evidence: PMID:22713602 Here we show that each of the six mutator proteins localizes to punctate foci at the periphery of germline nuclei. file:worm/mut-16/mut-16-deep-research-falcon.md In somatic contexts MUT-16 is more diffuse and Mutator foci are far less prominent. |
| GO:0035194 regulatory ncRNA-mediated post-transcriptional gene silencing | IMP PMID:12906791 A genome-wide screen identifies 27 genes involved in transpo... | ACCEPT | Summary: PMID:12906791 identified mut-16 in a genome-wide screen for genes involved in transposon silencing, demonstrating a role in gene silencing. MUT-16 is required for the mutator pathway that produces secondary siRNAs for post-transcriptional gene silencing. Reason: This is a core function of MUT-16. The mutator complex synthesizes secondary siRNAs (22G-RNAs) that mediate post-transcriptional gene silencing of transposons and other endogenous targets. PMID:12906791 demonstrates mut-16 mutants have defective transposon silencing, and later work confirms this is through the siRNA pathway. Supporting Evidence: PMID:12906791 We identified 27 such genes, among which are mut-16, a mutator that was previously found but not identified at the molecular level PMID:12906791 Interestingly, the transposon-silencing mechanism shares factors with the RNAi machinery. PMID:22713602 We propose that the mutator proteins and RRF-1 constitute an RNA processing compartment required for siRNA amplification and RNA silencing. file:worm/mut-16/mut-16-deep-research-falcon.md Functions in the **WAGO-class 22G-RNA branch** of RNAi downstream of primary triggers such as piRNAs and exogenous RNAi file:worm/mut-16/mut-16-deep-research-falcon.md A key mechanistic model in recent reviews is that primary targeting can trigger cleavage and then **pUGylation** (addition of poly(UG) tails) by **MUT-2/RDE-3**, which helps recruit RdRP activity to generate amplified secondary 22G-RNAs. |
| GO:0010526 transposable element silencing | IMP PMID:12906791 A genome-wide screen identifies 27 genes involved in transpo... | NEW | Summary: MUT-16 is required for transposon silencing in the C. elegans germline. PMID:12906791 identified mut-16 in a genome-wide screen for genes required to silence Tc1 transposon activity. Reason: This annotation is not currently in the GOA file but represents a core function of MUT-16. The original screen that named mut-16 as a MUTator gene was based on transposon activation phenotypes. This is a more specific annotation than the general gene silencing term. Supporting Evidence: PMID:12906791 To better understand the mechanism of transposon silencing, we performed a genome-wide RNAi screen for genes that, when silenced, cause transposition of Tc1 in the C. elegans germline. We identified 27 such genes, among which are mut-16, a mutator that was previously found but not identified at the molecular level file:worm/mut-16/mut-16-deep-research-falcon.md The Mutator/WAGO 22G-RNA system is widely framed as a **genome surveillance/defense** pathway that limits transposon expression/mobilization and supports fertility, with MUT-16 as a core scaffold. file:worm/mut-16/mut-16-deep-research-falcon.md the **Tc1** DNA transposon has **~32 intact copies** in the genome |
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