SID-1 domains important for dsRNA import inC. elegans

AbstractIn the nematodeCaenorhabditis elegans,RNA interference (RNAi) triggered by double-stranded RNA (dsRNA) spreads systemically to cause gene silencing throughout the organism and its progeny. We confirm thatCaenorhabditisnematode SID-1 orthologs have dsRNA transport activity and demonstrate that the SID-1 paralog CHUP-1 does not transport dsRNA. Sequence comparison of these similar proteins, in conjunction with analysis of loss-of-function missense alleles identifies several conserved 2-7 amino acid microdomains within the extracellular domain that are important for dsRNA transport. Among these missense alleles, we identify and characterize asid-1allele,qt95, which causes tissue-specific silencing defects most easily explained as a systemic RNAi export defect. However, we conclude from genetic and biochemical analyses thatsid-1(qt95)disrupts only import and speculate that the apparent export defect is caused by the cumulative effect of sequentially impaired dsRNA import steps.Thus, consistent with previous studies, we fail to detect a requirement forsid-1in dsRNA export, but demonstrate for the first time that SID-1 functions in the intestine to support environmental RNAi.