POLⅢ-derived non-coding RNAs acting as scaffolds and decoys

A large variety of eukaryotic small structured POLⅢ-derived non-coding RNAs (ncRNAs) have been described in the past.However,for only few,e.g.7SL and H1/MRP families,cellular functions are well understood.For the vast majority of these transcripts,cellular functions remain unknown.Recent findings on the role ofY RNAs and other POLⅢ-derived ncRNAs suggest an evolutionarily conserved function of these ncRNAs in the assembly and function of ribonucleoprotein complexes (RNPs).These RNPs provide cellular'machineries',which are essential for guiding the fate and function of a variety of RNAs.In this review,we summarize current knowledge on the role of POLⅢ-derived ncRNAs in the assembly and function of RNPs.We propose that these ncRNAs serve as scaffolding factors that'chaperone'RNA-binding proteins (RBPs) to form functional RNPs.ln addition or associated with this role,some small ncRNAs act as molecular decoys impairing the RBP-guided control of RNA fate by competing with other RNA substrates.This suggests that POLⅢ-derived ncRNAs serve essential and conserved roles in the assembly of larger RNPs and thus the control of gene expression by indirectly guiding the fate of mRNAs and lncRNAs.