Figure 1.

RNAi-facilitating features of C. elegans. A: Uptake of dsRNA from the environment is allowed in part by the action of transmembrane protein SID-1, promoting endocytosis of bound RNA. B: RNAi amplification. dsRNA molecules are processed to short “primary” siRNA (left). When an siRNA molecule binds to a target, additional target-complementary siRNAs can be generated after extension by RNA-dependent RNA polymerase and processing. C: SID-2 binds long dsRNA for endocytosis and secondary uptake into the cytoplasm by SID-1 (not shown). Note that cartoons are for illustration only and are not meant to represent relative size or molecular topology.