PABP is not essential for microRNA-mediated translational repression and deadenylation in vitro

MicroRNAs silence their complementary target genes via formation of the RNA‐induced silencing complex (RISC) that contains an Argonaute (Ago) protein at its core. It was previously proposed that GW182, an Ago‐associating protein, directly binds to poly(A)‐binding protein (PABP) and interferes with its function, leading to silencing of the target mRNAs. Here we show that Drosophila Ago1‐RISC induces silencing via two independent pathways: shortening of the poly(A) tail and pure repression of translation. Our data suggest that although PABP generally modulates poly(A) length and translation efficiency, neither PABP function nor GW182–PABP interaction is a prerequisite for these two silencing pathways. Instead, we propose that each of the multiple functional domains within GW182 has a potential for silencing, and yet they need to act together in the context of full‐length GW182 to exert maximal silencing. The mechanism by which miRNAs induce silencing of gene expression remains a matter of much debate. This study shows that maximal silencing is dependent on multiple concerted interactions in the context of the full‐length GW182 protein rather than single protein–protein associations.