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<title>Cytosolic help for mitochondrial defects - Coffee Break - NCBI Bookshelf</title>
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<meta name="robots" content="INDEX,FOLLOW,NOARCHIVE" /><meta name="citation_inbook_title" content="Coffee Break: Tutorials for NCBI Tools [Internet]" /><meta name="citation_title" content="Cytosolic help for mitochondrial defects" /><meta name="citation_publisher" content="National Center for Biotechnology Information (US)" /><meta name="citation_date" content="2000/12/04" /><meta name="citation_author" content="Laura Dean" /><meta name="citation_author" content="Johanna McEntyre" /><meta name="citation_fulltext_html_url" content="https://www.ncbi.nlm.nih.gov/books/NBK2327/" /><link rel="schema.DC" href="http://purl.org/DC/elements/1.0/" /><meta name="DC.Title" content="Cytosolic help for mitochondrial defects" /><meta name="DC.Type" content="Text" /><meta name="DC.Publisher" content="National Center for Biotechnology Information (US)" /><meta name="DC.Contributor" content="Laura Dean" /><meta name="DC.Contributor" content="Johanna McEntyre" /><meta name="DC.Date" content="2000/12/04" /><meta name="DC.Identifier" content="https://www.ncbi.nlm.nih.gov/books/NBK2327/" /><meta name="description" content="The mitochondrion has cut back its genome substantially since taking up residence in cells as a symbiont 1.5 billion years ago, but it retains its personal transcription, translation and protein-assembling systems, including its tRNA genes. Even so, the mitochondrion is not fully self-sufficient — to varying extents yeast, plants and protozoan cells can borrow nuclear-encoded tRNA molecules to ease the task of translating transcripts of their mitochondrial genes. New data indicate that nuclear-encoded tRNAs can even be used to salvage errors in mitochondrial transcripts." /><meta name="og:title" content="Cytosolic help for mitochondrial defects" /><meta name="og:type" content="book" /><meta name="og:description" content="The mitochondrion has cut back its genome substantially since taking up residence in cells as a symbiont 1.5 billion years ago, but it retains its personal transcription, translation and protein-assembling systems, including its tRNA genes. Even so, the mitochondrion is not fully self-sufficient — to varying extents yeast, plants and protozoan cells can borrow nuclear-encoded tRNA molecules to ease the task of translating transcripts of their mitochondrial genes. New data indicate that nuclear-encoded tRNAs can even be used to salvage errors in mitochondrial transcripts." /><meta name="og:url" content="https://www.ncbi.nlm.nih.gov/books/NBK2327/" /><meta name="og:site_name" content="NCBI Bookshelf" /><meta name="og:image" content="https://www.ncbi.nlm.nih.gov/corehtml/pmc/pmcgifs/bookshelf/thumbs/th-coffeebrk-lrg.png" /><meta name="twitter:card" content="summary" /><meta name="twitter:site" content="@ncbibooks" /><meta name="bk-non-canon-loc" content="/books/n/coffeebrk/A27/" /><link rel="canonical" href="https://www.ncbi.nlm.nih.gov/books/NBK2327/" /><link rel="stylesheet" href="/corehtml/pmc/css/figpopup.css" type="text/css" media="screen" /><link rel="stylesheet" href="/corehtml/pmc/css/bookshelf/2.26/css/books.min.css" type="text/css" /><link rel="stylesheet" href="/corehtml/pmc/css/bookshelf/2.26/css/books_print.min.css" type="text/css" /><style type="text/css">p a.figpopup{display:inline !important} .bk_tt {font-family: monospace} .first-line-outdent .bk_ref {display: inline} </style><script type="text/javascript" src="/corehtml/pmc/js/jquery.hoverIntent.min.js"> </script><script type="text/javascript" src="/corehtml/pmc/js/common.min.js?_=3.18"> </script><script type="text/javascript">window.name="mainwindow";</script><script type="text/javascript" src="/corehtml/pmc/js/bookshelf/2.26/book-toc.min.js"> </script><script type="text/javascript" src="/corehtml/pmc/js/bookshelf/2.26/books.min.js"> </script>
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<div class="pre-content"><div><div class="bk_prnt"><p class="small">NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.</p><p>Dean L, McEntyre J, editors. Coffee Break: Tutorials for NCBI Tools [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 1999-. </p></div></div></div>
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<div class="main-content lit-style" itemscope="itemscope" itemtype="http://schema.org/CreativeWork"><div class="meta-content fm-sec"><h1 id="_NBK2327_"><span class="title" itemprop="name">Cytosolic help for mitochondrial defects</span></h1><div class="subtitle">a novel method for importing tRNA into mitochondria in order to suppress mutations</div><p class="small">Created: <span itemprop="datePublished">December 4, 2000</span>.</p></div><div class="body-content whole_rhythm" itemprop="text"><p>The mitochondrion has cut back its genome substantially since taking up
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residence in cells as a symbiont 1.5 billion years ago, but it retains its
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personal transcription, translation and protein-assembling systems, including
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its tRNA genes. Even so, the mitochondrion is not fully self-sufficient — to varying extents yeast, plants and protozoan cells can borrow nuclear-encoded
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tRNA molecules to ease the task of translating transcripts of their mitochondrial genes. New data indicate that nuclear-encoded tRNAs can even be used to salvage errors in mitochondrial transcripts.</p><p>
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<a class="figpopup" href="/books/NBK2327/figure/A555/?report=objectonly" target="object" rid-figpopup="figA555" rid-ob="figobA555">Figure 1</a>
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</p><p>In the yeast <i>Saccharomyces cerevisiae,</i> only one tRNA (<sup>Lys</sup><sub>CUU</sub>) is carried into the mitochondrion, something it can do only if charged with an amino acid, and only if aided by cytosolic import factors. Among these factors is the precursor of the mitochondrial lysyl-tRNA synthetase (pre-MSK).</p><p>
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<a class="figpopup" href="/books/NBK2327/figure/A556/?report=objectonly" target="object" rid-figpopup="figA556" rid-ob="figobA556">Figure 2</a>
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</p><p>In a recent <a href="/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10988073&dopt=Abstract" ref="pagearea=body&targetsite=external&targetcat=link&targettype=uri"><u>publication</u></a>, researchers altered the aminoacylation identity of tRNA<sup>Lys</sup>
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<sub>CUU</sub> so that it was charged with methionine rather than lysine. Both in live yeast cells and in isolated mitochondria, the engineered tRNA could enter the mitochondrion, where the radiolabelled methionine charged on the imported tRNA was incorporated normally into mitochondrial proteins. A second, modified tRNA<sup>Lys</sup> version with alanine identity was also successfully used <i>in vivo</i> to suppress an <i>amber</i> (UAG) stop codon (a nonsense mutation) in the mitochondrial <i> COX2</i> gene.</p><p>Defects in mitochondrial (mt) DNA, caused by base substitutions or rearrangements in genes that encode proteins or tRNAs underlie a range of human pathologies (as discussed in the previous highlight).</p><p>Could the technique used to modify mitochondrial mutations be adapted for use in humans, given that import of nuclear-encoded tRNAs into mammalian mitochondria has never been seen? It seems so, because isolated human mitochondria imported the yeast tRNA<sup>Lys</sup>
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<sub>CUU</sub> and its derivatives, provided that the human cytosolic extracts were supplemented with the yeast pre-MSK. The foreign tRNA was functional on the translational apparatus of human mitochondria, just as in yeast.</p><p>This recent innovation might be useful for replacing non-functional tRNAs or for suppressing nonsense mutations in mtDNA.</p><p>Story contributed by Tanita Casci, <a href="http://www.nature.com/nrg/index.html" ref="pagearea=body&targetsite=external&targetcat=link&targettype=uri"><u>Nature Reviews Genetics</u></a>
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</p><p>
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</p><div id="A401" class="box"><h3><span class="title">Search Organelle Genome Resources</span></h3><p>Created: December 4, 2000</p><p>Click on the link below to start an html tutorial.</p><p>
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Evolution and the mitochondrial gene order of tRNAs</p></div><div class="bk_prnt_sctn"><h2>Figures</h2><div class="whole_rhythm bk_prnt_obj bk_first_prnt_obj"><div id="A555" class="figure bk_fig"><div class="graphic"><img src="/books/NBK2327/bin/cb17a_big.jpg" alt="Tertiary structure of tRNA." /></div><h3><span class="title">Tertiary structure of tRNA</span></h3><div class="caption"><p><br />The anticodon loop and stem of tRNA<sup>Lys</sup> is depicted in the image to the left. The three bases that compose the anticodon (in this example, "U-U-U") are highlighted in yellow.</p></div></div></div><div class="whole_rhythm bk_prnt_obj"><div id="A556" class="figure bk_fig"><div class="graphic"><img src="/books/NBK2327/bin/cb17b_big.jpg" alt="Mutation of the anticodon of tRNA." /></div><h3><span class="title">Mutation of the anticodon of tRNA</span></h3><div class="caption"><p><br />Outside of the mitochondria, tRNA<sup>Lys</sup>
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<sub>CUU</sub> is charged with lysine, its cognate amino acid. However, by changing the anticodon from C-U-U to C-A-U, the mutated tRNA is subsequently charged with methionine. To be able to track mutant tRNAs, an <sup>35</sup>S-radiolabelled methionine was used. This experiment demonstrated that aminoacylation was necessary for transport of tRNA into the mitochondria, although the identity of the amino acid that was charged onto the tRNA was less important.</p></div></div></div></div><div id="bk_toc_contnr"></div></div></div>
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<div class="post-content"><div><div class="half_rhythm"><a href="/books/about/copyright/">Copyright Notice</a></div><div class="small"><span class="label">Bookshelf ID: NBK2327</span></div><div style="margin-top:2em" class="bk_noprnt"><a class="bk_cntns" href="/books/n/coffeebrk/">Contents</a><div class="pagination bk_noprnt"><a class="active page_link prev" href="/books/n/coffeebrk/A28/" title="Previous page in this title">< Prev</a><a class="active page_link next" href="/books/n/coffeebrk/A26/" title="Next page in this title">Next ></a></div></div></div></div>
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