tRNAs marked with CCACCA are targeted for degradation

Koch Institute for Integrative Cancer Research and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Science (Impact Factor: 33.61). 11/2011; 334(6057):817-21. DOI: 10.1126/science.1213671
Source: PubMed


The CCA-adding enzyme [ATP(CTP):tRNA nucleotidyltransferase] adds CCA to the 3' ends of transfer RNAs (tRNAs), a critical step in tRNA biogenesis that generates the amino acid attachment site. We found that the CCA-adding enzyme plays a key role in tRNA quality control by selectively marking structurally unstable tRNAs and tRNA-like small RNAs for degradation. Instead of adding CCA to the 3' ends of these transcripts, CCA-adding enzymes from all three kingdoms of life add CCACCA. In addition, hypomodified mature tRNAs are subjected to CCACCA addition as part of a rapid tRNA decay pathway in vivo. We conjecture that CCACCA addition is a universal mechanism for controlling tRNA levels and preventing errors in translation.

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Available from: Joseph Whipple, Mar 26, 2014
    • "However, unlike mascRNA, the MEN β tRNA-like small RNA is structurally unstable (due to presence of a mismatch or multiple G–U wobbles in its acceptor stem) (Fig. 2B), causing it to be marked with CCACCA and rapidly degraded in most mouse and human cells [109] [110]. Interestingly, the MEN β tRNA-like small RNA is structurally stable in many other species, including monkeys, allowing it to be marked with CCA and accumulate in cells [109]. As its function is unknown, it is still unclear why the MEN β tRNA-like small RNA is stable in only some species. "
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    ABSTRACT: Most of the human genome is transcribed, yielding a complex network of transcripts that includes tens of thousands of long noncoding RNAs. Many of these transcripts have a 5' cap and a poly(A) tail, yet some of the most abundant long noncoding RNAs are processed in unexpected ways and lack these canonical structures. Here, I highlight the mechanisms by which several of these well-characterized noncoding RNAs are generated, stabilized, and function. The MALAT1 and MEN β (NEAT1_2) long noncoding RNAs each accumulate to high levels in the nucleus, where they play critical roles in cancer progression and the formation of nuclear paraspeckles, respectively. Nevertheless, MALAT1 and MEN β are not polyadenylated as the tRNA biogenesis machinery generates their mature 3' ends. In place of a poly(A) tail, these transcripts are stabilized by highly conserved triple helical structures. Sno-lncRNAs likewise lack poly(A) tails and instead have snoRNA structures at their 5' and 3' ends. Recent work has additionally identified a number of abundant circular RNAs generated by the pre-mRNA splicing machinery that are resistant to degradation by exonucleases. As these various transcripts use non-canonical strategies to ensure their stability, it is becoming increasingly clear that long noncoding RNAs may often be regulated by unique post-transcriptional control mechanisms. This article is part of a Special Issue entitled: Clues to long noncoding RNA taxonomy. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms 06/2015; DOI:10.1016/j.bbagrm.2015.06.003 · 6.33 Impact Factor
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    • "The CCA-3 is also required for tRNA quality control. The tandem C 74 C 75 A 76 C 77 C 78 A 79 -3 sequence, added onto the 3 -end of tRNA, acts as a degradation signal for dysfunctional tRNA molecules (Wilusz et al., 2011). The CCA-3 is synthesized and/or repaired by the CCA-adding enzyme, CTP:(ATP) tRNA nucleotidyltransferase (NT), using CTP and ATP as substrates (Deutscher, 1990; Weiner, 2004). "
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    ABSTRACT: The universal 3'-terminal CCA sequence of tRNA is built and/or synthesized by the CCA-adding enzyme, CTP:(ATP) tRNA nucleotidyltransferase. This RNA polymerase has no nucleic acid template, but faithfully synthesizes the defined CCA sequence on the 3'-terminus of tRNA at one time, using CTP and ATP as substrates. The mystery of CCA-addition without a nucleic acid template by unique RNA polymerases has long fascinated researchers in the field of RNA enzymology. In this review, the mechanisms of RNA polymerization by the remarkable CCA-adding enzyme and its related enzymes are presented, based on their structural features.
    Frontiers in Genetics 02/2014; 5:36. DOI:10.3389/fgene.2014.00036
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    • "The invariant CCA-3 0 is required for amino acid attachment onto the 3 0 end of the tRNA by aminoacyl-tRNA synthases (Sprinzl and Cramer, 1979), and for peptide-bond formation on ribosomes (Green and Noller, 1997; Kim and Green, 1999; Nissen et al., 2000). The CCA-3 0 is also required for tRNA quality control (Wilusz et al., 2011). "
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    ABSTRACT: The 3'-terminal CCA (CCA-3' at positions 74-76) of tRNA is synthesized by CCA-adding enzyme using CTP and ATP as substrates, without a nucleic acid template. In Aquifex aeolicus, CC-adding and A-adding enzymes collaboratively synthesize the CCA-3'. The mechanism of CCA-3' synthesis by these two enzymes remained obscure. We now present crystal structures representing CC addition onto tRNA by A. aeolicus CC-adding enzyme. After C74 addition in an enclosed active pocket and pyrophosphate release, the tRNA translocates and rotates relative to the enzyme, and C75 addition occurs in the same active pocket as C74 addition. At both the C74-adding and C75-adding stages, CTP is selected by Watson-Crick-like hydrogen bonds between the cytosine of CTP and conserved Asp and Arg residues in the pocket. After C74C75 addition and pyrophosphate release, the tRNA translocates further and drops off the enzyme, and the CC-adding enzyme terminates RNA polymerization.
    Structure 12/2013; 22(2). DOI:10.1016/j.str.2013.12.002 · 5.62 Impact Factor
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