The NIP proteins: Inhibitors of nuclear RNA interference

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The RNA interference (RNAi) pathways instigate gene silencing through transcriptional and post-transcriptional mechanisms. SiRNAs of endogenous and exogenous origins are loaded onto specialized cytoplasmic and nuclear Argonautes, which in turn direct gene-silencing complexes. Loading of nuclear Argonautes results in their nuclear translocation, and in recruitment of effector complexes, which mediate the deposition of silencing chromatin marks on target loci. We discovered the family of uncharacterized Nuclear Argonaute-Interacting Proteins (NIP-1, NIP-2 will be examined), which stably interact with NRDE-3. NIP proteins encode a conserved P-loop containing nucleoside triphosphate hydrolase (NTPase) domain. Loss-of-function alleles specifically enhance nuclear RNAi and NIP-1 overexpression results in refraction, while having little effect on cytoplasmic RNAi targets. NIP-1 interacts with unloaded NRDE-3, and does not interact with small RNAs.