Proteomic and functional analysis of Argonaute-containing mRNA-protein complexes in human cells

Members of the Argonaute ( Ago) protein family associate with small RNAs and have important roles in RNA silencing. Here, we analysed Ago1- and Ago2- containing protein complexes in human cells. Separation of Ago- associated messenger ribonucleoproteins ( mRNPs) showed that Ago1 and Ago2 reside in three complexes with distinct Dicer and RNA- induced silencing complex activities. A comprehensive proteomic analysis of Ago- containing mRNPs identified a large number of proteins involved in RNA metabolism. By using co- immunoprecipitation experiments followed by RNase treatment, we biochemically mapped interactions within Ago mRNPs. Using reporter assays and knockdown experiments, we showed that the putative RNA- binding protein RBM4 is required for microRNA- guided gene regulation.