| Primordial soup or vinaigrette: did the RNA world evolve at acidic pH? | |
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MedLine Citation:
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PMID: 22264281 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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ABSTRACT: BACKGROUND: The RNA world concept has wide, though certainly not unanimous, support within the origin-of-life scientific community. One view is that life may have emerged as early as the Hadean Eon 4.3-3.8 billion years ago with an atmosphere of high CO2 producing an acidic ocean of the order of pH 3.5-6. Compatible with this scenario is the intriguing proposal that life arose near alkaline (pH 9-11) deep-sea hydrothermal vents like those of the 'Lost City', with the interface with the acidic ocean creating a proton gradient sufficient to drive the first metabolism. However, RNA is most stable at pH 4-5 and is unstable at alkaline pH, raising the possibility that RNA may have first arisen in the acidic ocean itself (possibly near an acidic hydrothermal vent), acidic volcanic lake or comet pond. As the Hadean Eon progressed, the ocean pH is inferred to have gradually risen to near neutral as atmospheric CO2 levels decreased. PRESENTATION OF THE HYPOTHESIS: We propose that RNA is well suited for a world evolving at acidic pH. This is supported by the enhanced stability at acidic pH of not only the RNA phosphodiester bond but also of the aminoacyl-(t)RNA and peptide bonds. Examples of in vitro-selected ribozymes with activities at acid pH have recently been documented. The subsequent transition to a DNA genome could have been partly driven by the gradual rise in ocean pH, since DNA has greater stability than RNA at alkaline pH, but not at acidic pH. TESTING THE HYPOTHESIS: We have proposed mechanisms for two key RNA world activities that are compatible with an acidic milieu: (i) non-enzymatic RNA replication of a hemi-protonated cytosine-rich oligonucleotide, and (ii) specific aminoacylation of tRNA/hairpins through triple helix interactions between the helical aminoacyl stem and a single-stranded aminoacylating ribozyme. IMPLICATIONS OF THE HYPOTHESIS: Our hypothesis casts doubt on the hypothesis that RNA evolved in the vicinity of alkaline hydrothermal vents. The ability of RNA to form protonated base pairs and triples at acidic pH suggests that standard base pairing may not have been a dominant requirement of the early RNA world. Reviewers This article was reviewed by Eugene Koonin, Anthony Poole and Charles Carter (nominated by David Ardell). |
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Authors:
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Harold S Bernhardt; Warren P Tate |
Publication Detail:
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Type: JOURNAL ARTICLE Date: 2012-1-20 |
Journal Detail:
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Title: Biology direct Volume: 7 ISSN: 1745-6150 ISO Abbreviation: - Publication Date: 2012 Jan |
Date Detail:
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Created Date: 2012-1-23 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 101258412 Medline TA: Biol Direct Country: - |
Other Details:
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Languages: ENG Pagination: 4 Citation Subset: - |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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