The DGCR8-UGU interaction in microRNA biogenesis

Human Microprocessor is a trimeric complex composed of the RNase III enzyme, DROSHA, and a dimer of DGCR8 (its cofactor). Microprocessor initiates the biogenesis of microRNA by processing primary microRNAs (pri-miRNAs), during which, its cleavage efficiency and accuracy are enhanced because DGCR8 interacts with the apical UGU motif of pri-miRNAs. However, the mechanism of DGCR8-UGU interaction and influence of this interaction on the expression of cellular miRNA are still elusive. In this study, we demonstrated that the Rhed domain (i.e., the RNA-binding heme domain, amino acids 285-478) of DGCR8 is sufficient to recognize and interact with UGU. In addition, we identified three amino acid residues in Rhed (amino acids 361-363), which are critical for the UGU interaction, and we showed that these residues are essential for the Microprocessor complex to accurately and efficiently process pri-miRNAs in vitro. Furthermore, we found that within the DGCR8 dimer, the UGU-binding site from just one monomer is capable of discriminating between UGU- and non-UGU-containing pri-miRNAs. Finally, we showed that these amino acids are more important for the expression of UGU miRNAs than non-UGU miRNAs in human cells. This study improves our understanding of the substrate-recognizing mechanism of DGCR8, and implicates the roles of this recognition in differentiating miRNA expression in human cells. Overall design: DGCR8-KO cells were transfected with pCK empty, pCK-DGCR8 WT or pCK-DGCR8 mut1 plasmid. Small RNA sequencing libraries of the transfected DGCR8-KO cells were generated using the TruSeq Small RNA Library Prep kit. The experiment was repeated three times.