The bulges control in pri-miRNA processing in the position and strand-dependent manner

The microRNA (miRNA) biogenesis is responsible for the production of miRNAs that play critical roles in gene expression and numerous human diseases. The adequate biogenesis of miRNAs is largely determined by the efficiency and fidelity of primary microRNA (pri-miRNA) processing by Microprocessor. Here, we investigated the roles of a secondary RNA element, an RNA bulge, in pri-miRNA processing. We discovered that the 3p-strand bulges in positions 7-9 from the Microprocessor cleavage sites (midB_7-9) contributes to determining the cleavage sites of Microprocessor, the 5p- and 3p-strand bugles in positions 10-12 (midB_10-12) blocked the unproductive cleavage, and the 3p-strand bulges in positions 6-7 (seedB) inhibited the productive cleavage of Microprocessor. The 5p-strand midB_10-12 was found enriched and conserved in many pri-miRNAs of humans and other organisms. In addition, by analyzing the published Microprocessor-RNA structure and doing mutagenesis, we identified several amino acid residues of Microprocessor that explains a structure basis for the processing inhibition caused by seedB. The revealed functions of bulges in our study improves our understanding of the pri-miRNA processing by Microprocessor and implies their roles in regulating miRNA expression. HCT116 cells were transfected with pcDNA3.0 plasmids encoding pri-mir-342 or its variants. Small RNA sequencing libraries of the transfected cells were generated. The experiment was repeated three times.