Microprocessor, composed of DROSHA and DGCR8, processes primary microRNAs (pri-miRNAs) in miRNA biogenesis. Its cleavage efficiency and accuracy are enhanced because DGCR8 interacts with the apical UGU motif of pri-miRNAs. However, the mechanism and influence of DGCR8–UGU interaction on cellular miRNA expression are still elusive. In this study, we demonstrated that Rhed (i.e., the RNA-binding heme domain, amino acids 285–478) of DGCR8 interacts with UGU. In addition, we identified three amino acids 461–463 in Rhed, which are critical for the UGU interaction and essential for Microprocessor to accurately and efficiently process UGU-pri-miRNAs in vitro and UGU-miRNA expression in human cells. Furthermore, we found that within the DGCR8 dimer, the amino acids 461–463 from one monomer are capable of discriminating between UGU- and noUGU-pri-miRNAs. Our findings improve the current understanding of the substrate-recognizing mechanism of DGCR8 and implicate the roles of this recognition in differentiating miRNA expression in human cells.

由DROSHA和DGCR8组成的微处理器在miRNA生物发生过程中处理初级microRNA（pri-miRNA）。由于DGCR8与pri-miRNA的顶端UGU基元相互作用，因此其切割效率和准确性得以提高。然而，DGCR8–UGU相互作用对细胞miRNA表达的机制和影响仍然难以捉摸。在这项研究中，我们证明了DGCR8的Rhed（即RNA结合血红素结构域，氨基酸285-478）与UGU相互作用。此外，我们在Rhed中鉴定了三个氨基酸461-463，这对于UGU相互作用至关重要，对于微处理器在体外准确有效地处理UGU-pri-miRNA和在人类细胞中表达UGU-miRNA至关重要。此外，我们发现在DGCR8二聚体中，一种单体的氨基酸461-463能够区分UGU-和noUGU-pri-miRNA。