SYNCRIP, a new player in pri-let-7a processing

microRNAs (miRNAs), a class of small and endogenous molecules that control gene expression, are broadly involved in biological processes. Although a number of cofactors that assist or antagonize let-7 miRNA biogenesis are well-established, more auxiliary factors remain to be investigated. Here, we identified SYNCRIP (Synaptotagmin Binding Cytoplasmic RNA Interacting Protein) as a new player for let-7a miRNA. SYNCRIP interacts with pri-let-7a both in vivo and in vitro. Knockdown of SYNCRIP impairs, while overexpression of SYNCRIP promotes, the expression of let-7a miRNA. A broad miRNA profiling analysis revealed that silencing of SYNCRIP regulates the expression of a set of mature miRNAs positively or negatively. In addition, SYNCRIP is associated with microprocessor complex and promotes the processing of pri-let-7a. Strikingly, the terminal loop of pri-let-7a was shown to be the main contributor for its interaction with SYNCRIP. Functional studies demonstrated that the SYNCRIP RRM2–3 domain can promote the processing of pri-let-7a. Structure-based alignment of RRM2–3 with other RNA binding proteins identified the residues likely to participate in protein–RNA interactions. Taken together, these findings suggest the promising role that SYNCRIP plays in miRNA regulation, thus providing insights into the function of SYNCRIP in eukaryotic development.