Abstract
The GW182/TNRC6 family of proteins are central scaffolds that link microRNA-associated Argonaute proteins to the cytoplasmic decay machinery for targeted mRNA degradation processes. Although nuclear roles for the GW182/TNRC6 proteins are unknown, recent reports have demonstrated nucleocytoplasmic shuttling activity that utilises the importin-α and importin-β transport receptors for nuclear translocation. Here we describe the structure of mouse importin-α in complex with the TNRC6A nuclear localisation signal peptide. We further show that the interactions observed between TNRC6A and importin-α are conserved between mouse and human complexes. Our results highlight the ability of monopartite cNLS sequences to maximise contacts at the importin-α major binding site, as well as regions outside the main binding cavities.
Highlights
MicroRNAs are master regulators of post-transcriptional gene expression, playing an important role in myriad cellular processes. miRNAs are loaded onto Argonaute (Ago) proteins to form the core of miRNA-induced silencing complexes, and exert their function through base complementarity, predominantly at 3’ untranslated regions (UTRs) of target mRNAs [1,2,3]
The GW182/TNRC6 family proteins are characterized by an abundance of (G/S/T)W(G/S/T) motifs that are located throughout the length of the protein (Fig 1A); while the N-terminal GW motifs confer binding to Ago proteins [5, 8, 9], the C-terminal GW repeats are important for the recruitment of the PAN2-PAN3 and CCR4-NOT deadenylase complexes [10,11,12,13,14,15] for poly(A) tail removal, a process termed deadenylation
In vitro GST pull-downs have shown a direct interaction between TNRC6A and human Impα, these assays were performed in the context of the full-length protein and in the presence of Impβ, which forms additional contacts with TNRC6A outside of the described classical NLSs (cNLSs) region [33]
Summary
MicroRNAs (miRNAs) are master regulators of post-transcriptional gene expression, playing an important role in myriad cellular processes. miRNAs are loaded onto Argonaute (Ago) proteins to form the core of miRNA-induced silencing complexes (miRISCs), and exert their function through base complementarity, predominantly at 3’ untranslated regions (UTRs) of target mRNAs [1,2,3].
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