Identification of Novel Argonaute-Associated Proteins

SummaryRNA silencing processes are guided by small RNAs known as siRNAs and microRNAs (miRNAs) 1, 2, 3 and 4. They reside in ribonucleoprotein complexes, which guide the cleavage of complementary mRNAs 3 and 4 or affect stability and translation of partial complementary mRNAs 1, 2 and 5. Argonaute (Ago) proteins are at the heart of silencing effector complexes and bind the single-stranded siRNA and miRNA 4 and 6. Our biochemical analysis revealed that Ago2 is present in a pre-miRNA processing complex that is able to transfer the miRNA into a target-mRNA cleaving complex. To gain insight into the function and composition of RNA silencing complexes, we purified Ago1- and Ago2-containing complexes from human cells. Several known Ago1- and/or Ago2-associated proteins including Dicer were identified, but also two novel factors, the putative RNA helicase MOV10, and the RNA recognition motif (RRM)-containing protein TNRC6B/KIAA1093. The new proteins localize, similar to Ago proteins, to mRNA-degrading cytoplasmic P bodies, and they are functionally required to mediate miRNA-guided mRNA cleavage.