Human Microprocessor is a trimeric complex, composed of a RNase Ill - Drosha and the DGCR8 (DiGeorge syndrome chromosomal region 8) dimer, that processes primary microRNAs (pri-miRNAs) to initiate microRNA (miRNA) biogenesis. Drosha is a catalytic subunit, while DGCR8 functions as a cofactor. DGCR8 recognizes the loop and apical UGU motif of pri-miRNAs, thereby enhancing the efficiency and accuracy of Microprocessor cleavage. However, the molecular mechanism of DGCR8-UGU interaction and its influences on the cellular miRNA expression are elusive. In this study, I discover that RNA-binding heme domain (Rhed, amino acids 285^th -478^th) of DGCR8 contains the UGU-binding sites. I further identify that 461-463 residues of Rhed are responsible for the UGU recognition, which in turn, determine...[ Read more ]

Human Microprocessor is a trimeric complex, composed of a RNase Ill - Drosha and the DGCR8 (DiGeorge syndrome chromosomal region 8) dimer, that processes primary microRNAs (pri-miRNAs) to initiate microRNA (miRNA) biogenesis. Drosha is a catalytic subunit, while DGCR8 functions as a cofactor. DGCR8 recognizes the loop and apical UGU motif of pri-miRNAs, thereby enhancing the efficiency and accuracy of Microprocessor cleavage. However, the molecular mechanism of DGCR8-UGU interaction and its influences on the cellular miRNA expression are elusive. In this study, I discover that RNA-binding heme domain (Rhed, amino acids 285^th -478^th) of DGCR8 contains the UGU-binding sites. I further identify that 461-463 residues of Rhed are responsible for the UGU recognition, which in turn, determine the accuracy of pri-miRNA processing in vitro. Interestingly, I demonstrate that each subunit of DGCR8 dimer contains an UGU-binding site that is able to stimulate the accuracy and efficiency of the Drosha cleavage. Furthermore, the rescue DGCR8-knockout experiments with the different the DGCR8 variant defective in UGU recognition, reveals the physiological functions of this interaction to miRNA expression in vivo. This study highlights the molecular mechanism and biological significance of the specific DGCR8-UGU interaction in miRNA biogenesis.