Mono-Uridylation of Pre-MicroRNA as a Key Step in the Biogenesis of Group II let-7 MicroRNAs

• Published in: Cell Vol. 151; no. 3; pp. 521 - 532
• Main Authors: Heo, Inha, Ha, Minju, Lim, Jaechul, Yoon, Mi-Jeong, Park, Jong-Eun, Kwon, S. Chul, Chang, Hyeshik, Kim, V. Narry
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 26-10-2012
• Subjects: Base Sequence; biogenesis; DNA-Binding Proteins - metabolism; double-stranded RNA; embryonic stem cells; HeLa Cells; Humans; microRNA; MicroRNAs - metabolism; Molecular Sequence Data; mRNA Cleavage and Polyadenylation Factors; Polynucleotide Adenylyltransferase - metabolism; ribonucleases; RNA Nucleotidyltransferases - metabolism; RNA Processing, Post-Transcriptional; RNA-Binding Proteins - metabolism; RNases; somatic cells; transferases; Uridine Monophosphate - metabolism
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2012.09.022

RNase III Drosha initiates microRNA (miRNA) maturation by cleaving a primary miRNA transcript and releasing a pre-miRNA with a 2 nt 3′ overhang. Dicer recognizes the 2 nt 3′ overhang structure to selectively process pre-miRNAs. Here, we find that, unlike prototypic pre-miRNAs (group I), group II pre-miRNAs acquire a shorter (1 nt) 3′ overhang from Drosha processing and therefore require a 3′-end mono-uridylation for Dicer processing. The majority of let-7 and miR-105 belong to group II. We identify TUT7/ZCCHC6, TUT4/ZCCHC11, and TUT2/PAPD4/GLD2 as the terminal uridylyl transferases responsible for pre-miRNA mono-uridylation. The TUTs act specifically on dsRNAs with a 1 nt 3′ overhang, thereby creating a 2 nt 3′ overhang. Depletion of TUTs reduces let-7 levels and disrupts let-7 function. Although the let-7 suppressor, Lin28, induces inhibitory oligo-uridylation in embryonic stem cells, mono-uridylation occurs in somatic cells lacking Lin28 to promote let-7 biogenesis. Our study reveals functional duality of uridylation and introduces TUT7/4/2 as components of the miRNA biogenesis pathway.
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▸ Unlike canonical group I miRNA precursors, group II members have a 1 nt 3′ overhang ▸ Mono-uridylation of group II pre-let-7 promotes Dicer processing ▸ TUT7, TUT4, and TUT2 catalyze pre-let-7 mono-uridylation in cells lacking Lin28 ▸ Lin28 induces oligo-uridylation to inhibit let-7 processing
Group II precursors require mono-uridylation by TUTases to create the overhang of 2 nt required for Dicer processing. In the presence of Lin28, let-7 is preferably oligo-uridylated by TUT4 promoting its degradation, revealing the functional duality of uridylation.