PMID:12906791

A genome-wide screen identifies 27 genes involved in transposon silencing in C. elegans.

mut-16 was identified in a genome-wide RNAi screen for transposon silencing factors

"We identified 27 such genes, among which are mut-16, a mutator that was previously found but not identified at the molecular level"
mut-16 mutants show activation of Tc1 transposon in the germline

"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."
The transposon-silencing mechanism shares factors with the RNAi machinery

"Interestingly, the transposon-silencing mechanism shares factors with the RNAi machinery."

PMID:22713602

MUT-16 promotes formation of perinuclear mutator foci required for RNA silencing in the C. elegans germline.

MUT-16 is a Q/N-rich protein required for Mutator foci formation

"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."
Mutator foci are punctate foci at the periphery of germline nuclei

"Here we show that each of the six mutator proteins localizes to punctate foci at the periphery of germline nuclei."
Mutator foci are adjacent to but distinct from P granules

"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."
RdRP RRF-1 colocalizes with MUT-16 at Mutator foci

"The RdRP RRF-1 colocalizes with MUT-16 at Mutator foci, suggesting a role for Mutator foci in siRNA amplification."
Genes with high siRNA levels are disproportionally affected in mut-16 mutants

"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."
Mutator foci are required for siRNA amplification

"We propose that the mutator proteins and RRF-1 constitute an RNA processing compartment required for siRNA amplification and RNA silencing."

PMID:24684932

MUT-14 and SMUT-1 DEAD box RNA helicases have overlapping roles in germline RNAi and endogenous siRNA formation.

More than 2,000 genes are targeted by the mutator complex

"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."
MUT-16 nucleates the mutator complex

"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."
The mutator complex localizes to Mutator foci at the nuclear periphery

"The mutator complex localizes to Mutator foci adjacent to P granules at the nuclear periphery in germ cells."

PMID:32338603

A tudor domain protein, SIMR-1, promotes siRNA production at piRNA-targeted mRNAs in C. elegans.

Mutator foci are phase-separated condensates

"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."
Mutator foci are sites of mutator complex-dependent siRNA amplification

"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."
SIMR-1 foci are distinct from but adjacent to Mutator foci

"SIMR-1 also localizes to distinct subcellular foci adjacent to P granules and Mutator foci, two phase-separated condensates"

file:worm/mut-16/mut-16-deep-research-falcon.md

Falcon deep research report on mut-16 (C. elegans)

MUT-16 is a low-complexity, intrinsically disordered scaffold protein that nucleates perinuclear Mutator foci and organizes the germline Mutator complex, a small-RNA amplification module required for robust RNA silencing.

"a **low-complexity, intrinsically disordered scaffold protein** that **nucleates perinuclear"
MUT-16 is not a catalytic enzyme; its primary function is structural and organizational, concentrating and coordinating the enzymatic and RNA-binding factors that generate secondary 22G-RNAs.

"MUT-16 is **not an enzyme** with a defined catalytic reaction; instead, its primary function is **structural/organizational**"
A C-terminal disordered region (JKL; aa ~773-1050), ~70% disordered, is necessary and sufficient for Mutator-foci assembly.

"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."
Distinct MUT-16 regions recruit and localize different Mutator complex clients, including MUT-2/RDE-3, MUT-7, RDE-2, MUT-14, MUT-15, RRF-1, RDE-8, and NYN-1/2.

"CRISPR deletion mapping and interaction/localization assays identify **distinct MUT-16 regions** that mediate recruitment/localization of different Mutator complex proteins (e.g., MUT-2, MUT-7, RDE-2, MUT-14, MUT-15, RRF-1, RDE-8, NYN-1/2)."
Mutator foci behave as liquid-liquid phase-separated condensates (spherical morphology, 1,6-hexanediol and temperature sensitivity, concentration-threshold behavior, partial FRAP recovery).

"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."
FRAP of MUT-16::GFP foci showed t1/2 = 7.2 +/- 1.0 s and recovery to ~35% of pre-bleach intensity, consistent with mixed mobile and immobile condensate fractions.

"FRAP of MUT-16::GFP foci (whole-focus bleaching) showed **t1/2 = 7.2 ± 1.0 s (SEM; n=5)** and recovery to **~35%** of pre-bleach intensity"
MUT-16 localizes to punctate perinuclear foci throughout the germline, adjacent to but compositionally distinct from P granules; in somatic contexts it is more diffuse and foci are far less prominent.

"MUT-16 localizes to **punctate perinuclear foci** throughout the germline."
MUT-16 functions in the WAGO-class 22G-RNA branch of RNAi, downstream of primary triggers such as piRNAs and exogenous RNAi; target cleavage and pUGylation by MUT-2/RDE-3 mark RNAs for RdRP-dependent secondary 22G-RNA synthesis.

"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."
The Mutator/WAGO 22G-RNA system is a genome surveillance/defense pathway that limits transposon expression and mobilization and supports fertility, with MUT-16 as a core scaffold.

"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."
In mut-16 mutants, ~2,300 mutator-target genes showed >3-fold depletion of mutator-dependent 22G-RNAs, quantifying the global requirement for MUT-16 in secondary siRNA production.

"One study baseline reports that **~2,300 mutator-target genes** showed **>3-fold depletion** of mutator-dependent 22G-RNAs in **mut-16**."