Argonaute protein binding Met-tRNAiMet represses translation initiation

Initiation factor 2 (eIF2) delivering the initiator methionine transfer RNA (Met-tRNAiMet) to the ribosome is a conserved key step in translation initiation. Argonaute (Ago) proteins were initially identified as eukaryotic translation initiation factor 2C,2 (EIF2C2). In the past 2 decades, Argonaute were extensively studied as a core component of RNA induced gene silencing, although various model raised the exact mechanism of Ago in translation repression remains elusive. Here we found Ago protein directly bind Met- tRNAiMet independent of miRNA binding, which interfere the formation of the ternary complex eIF2–GTP–Met- tRNAiMet. Ago proteins can solely inhibit protein synthesis via competing tRNAiMet with eIF2. Our findings elucidate a physical link between Ago and tRNAiMet and provide mechanistic insight into translation repression by Ago proteins. Overall design: RNA interactome of Ago2 in light ribonucleoprotein or polysome fractions of sucrose gradient