4x4q
From Proteopedia
Crystal structure of the A.fulgidus CCA-adding enzyme in complex with a G70A arginyl-tRNA minihelix ending in CCAC and CTP
Structural highlights
FunctionCCA_ARCFU Catalyzes the addition and repair of the essential 3'-terminal CCA sequence in tRNAs without using a nucleic acid template. Adds these three nucleotides in the order of C, C, and A to the tRNA nucleotide-73, using CTP and ATP as substrates and producing inorganic pyrophosphate.[1] Publication Abstract from PubMedTranscription in eukaryotes produces a number of long noncoding RNAs (lncRNAs). Two of these, MALAT1 and Menbeta, generate a tRNA-like small RNA in addition to the mature lncRNA. The stability of these tRNA-like small RNAs and bona fide tRNAs is monitored by the CCA-adding enzyme. Whereas CCA is added to stable tRNAs and tRNA-like transcripts, a second CCA repeat is added to certain unstable transcripts to initiate their degradation. Here, we characterize how these two scenarios are distinguished. Following the first CCA addition cycle, nucleotide binding to the active site triggers a clockwise screw motion, producing torque on the RNA. This ejects stable RNAs, whereas unstable RNAs are refolded while bound to the enzyme and subjected to a second CCA catalytic cycle. Intriguingly, with the CCA-adding enzyme acting as a molecular vise, the RNAs proofread themselves through differential responses to its interrogation between stable and unstable substrates. On-Enzyme Refolding Permits Small RNA and tRNA Surveillance by the CCA-Adding Enzyme.,Kuhn CD, Wilusz JE, Zheng Y, Beal PA, Joshua-Tor L Cell. 2015 Feb 12;160(4):644-58. doi: 10.1016/j.cell.2015.01.005. Epub 2015 Jan, 29. PMID:25640237[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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