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Proc Biol Sci. 2001 Mar 7; 268(1466): 493–497.
PMCID: PMC1088632

High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes.


The causes of the variation between genomes in their guanine (G) and cytosine (C) content is one of the central issues in evolutionary genomics. The thermal adaptation hypothesis conjectures that, as G:C pairs in DNA are more thermally stable than adenonine:thymine pairs, high GC content may he a selective response to high temperature. A compilation of data on genomic GC content and optimal growth temperature for numerous prokaryotes failed to demonstrate the predicted correlation. By contrast, the GC content of Structural RNAs is higher at high temperatures. The issue that we address here is whether more freely evolving sites in exons (i.e. codonic third positions) evolve in the same manner as genomic DNA as a whole, Showing no correlated response, or like structural RNAs showing a strong correlation. The latter pattern would provide strong support for the thermal adaptation hypothesis, as the variation in GC content between orthologous genes is typically most profoundly seen at codon third sites (GC3). Simple analysis of completely sequenced prokaryotic genomes shows that GC3, but not genomic GC, is higher on average in thermophilic species. This demonstrates, if nothing else, that the results from the two measures cannot be presumed to be the same. A proper analysis, however, requires phylogenetic control. Here, therefore, we report the results of a comparative analysis of GC composition and optimal growth temperature for over 100 prokaryotes. Comparative analysis fails to show, in either Archea or Eubacteria, any hint of connection between optimal growth temperature and GC content in the genome as a whole, in protein-coding regions or, more crucially at GC. Conversely, comparable analysis confirms that GC content of structural RNA is strongly correlated with optimal temperature. Against the expectations of the thermal adaptation hypothesis, within prokaryotes GC content in protein-coding genies, even at relatively freely evolving sites, cannot be considered an adaptation to the thermal environment.

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  • Bernardi G. Isochores and the evolutionary genomics of vertebrates. Gene. 2000 Jan 4;241(1):3–17. [PubMed]
  • Bernardi G, Bernardi G. Compositional constraints and genome evolution. J Mol Evol. 1986;24(1-2):1–11. [PubMed]
  • Bruno WJ, Socci ND, Halpern AL. Weighted neighbor joining: a likelihood-based approach to distance-based phylogeny reconstruction. Mol Biol Evol. 2000 Jan;17(1):189–197. [PubMed]
  • Clay O, Cacciò S, Zoubak S, Mouchiroud D, Bernardi G. Human coding and noncoding DNA: compositional correlations. Mol Phylogenet Evol. 1996 Feb;5(1):2–12. [PubMed]
  • Galtier N, Lobry JR. Relationships between genomic G+C content, RNA secondary structures, and optimal growth temperature in prokaryotes. J Mol Evol. 1997 Jun;44(6):632–636. [PubMed]
  • Grayling RA, Sandman K, Reeve JN. Histones and chromatin structure in hyperthermophilic Archaea. FEMS Microbiol Rev. 1996 May;18(2-3):203–213. [PubMed]
  • Harvey PH, Purvis A. Comparative methods for explaining adaptations. Nature. 1991 Jun 20;351(6328):619–624. [PubMed]
  • Hughes S, Zelus D, Mouchiroud D. Warm-blooded isochore structure in Nile crocodile and turtle. Mol Biol Evol. 1999 Nov;16(11):1521–1527. [PubMed]
  • Kagawa Y, Nojima H, Nukiwa N, Ishizuka M, Nakajima T, Yasuhara T, Tanaka T, Oshima T. High guanine plus cytosine content in the third letter of codons of an extreme thermophile. DNA sequence of the isopropylmalate dehydrogenase of Thermus thermophilus. J Biol Chem. 1984 Mar 10;259(5):2956–2960. [PubMed]
  • Maidak BL, Cole JR, Lilburn TG, Parker CT, Jr, Saxman PR, Stredwick JM, Garrity GM, Li B, Olsen GJ, Pramanik S, et al. The RDP (Ribosomal Database Project) continues. Nucleic Acids Res. 2000 Jan 1;28(1):173–174. [PMC free article] [PubMed]
  • Muto A, Osawa S. The guanine and cytosine content of genomic DNA and bacterial evolution. Proc Natl Acad Sci U S A. 1987 Jan;84(1):166–169. [PMC free article] [PubMed]
  • Purvis A, Rambaut A. Comparative analysis by independent contrasts (CAIC): an Apple Macintosh application for analysing comparative data. Comput Appl Biosci. 1995 Jun;11(3):247–251. [PubMed]
  • Salinas J, Matassi G, Montero LM, Bernardi G. Compositional compartmentalization and compositional patterns in the nuclear genomes of plants. Nucleic Acids Res. 1988 May 25;16(10):4269–4285. [PMC free article] [PubMed]
  • Wada A, Suyama A. Local stability of DNA and RNA secondary structure and its relation to biological functions. Prog Biophys Mol Biol. 1986;47(2):113–157. [PubMed]
  • Winter G, Koch GL, Hartley BS, Barker DG. The amino acid sequence of the tyrosyl-tRNA synthetase from Bacillus stearothermophilus. Eur J Biochem. 1983 May 2;132(2):383–387. [PubMed]

Articles from Proceedings of the Royal Society B: Biological Sciences are provided here courtesy of The Royal Society


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