A four-column theory for the origin of the triplet code
2009 April 26
In a latest Biology Direct paper Paul G Higgs proposed a ‘four-column’ theory for the origin of the genetic code. Theory suggest that subdivision of codon blocks gave rise to an optimized code. Unlike previously proposed coevolution theory where genetic code evolution predicted are usually not favored by selection, in ‘four-column’ theory major driving force during code evolution process is positive selection which maintain increased diversity and functionality of the proteins, minimization of translational error appears to be only a secondary factor although current code is fully optimized with respect to translational error. Further this theory suggests that
(i) The earliest amino acids in the code were those that are easiest to synthesize non-biologically, namely Gly, Ala, Asp, Glu and Val. (ii) These amino acids are assigned to codons with G at first position. Therefore the first code may have used only these codons. (iii) The code rapidly developed into a four-column code where all codons in the same column coded for the same amino acid: NUN = Val, NCN = Ala, NAN = Asp and/or Glu, and NGN = Gly. (iv) Later amino acids were added sequentially to the code by a process of subdivision of codon blocks in which a subset of the codons assigned to an early amino acid were reassigned to a later amino acid. (v) Later amino acids were added into positions formerly occupied by amino acids with similar properties because this can occur with minimal disruption to the proteins already encoded by the earlier code. As a result, the properties of the amino acids in the final code retain a four-column pattern that is a relic of the earliest stages of code evolution.
Proposed four-column structure of the earliest genetic code
Possible evolution of the four-column code via subdivision of codon blocksUsing a cost function and a barrier function, theory predicts that that new amino acids can be added into positions previously occupied by amino acids with similar properties. This is because, when amino acids are added in this way, there is minimal disruption to the protein sequences that had already evolved under the previous code.
Reference:
Higgs, P. (2009). A four-column theory for the origin of the genetic code: tracing the evolutionary pathways that gave rise to an optimized code Biology Direct, 4 (1) DOI: 10.1186/1745-6150-4-16
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Theory for the origin of the triplet code in DNA – fantastically simple and elegant!l http://is.gd/uGYG
Theory for the origin of the triplet code in DNA – fantastically simple and elegant!l http://is.gd/uGYG
A four-column theory for the origin of the triplet code http://tinyurl.com/ctlpe6
A four-column theory for the origin of the triplet code: In a latest Biology Direct paper Paul G Higgs proposed .. http://tinyurl.com/d6wk6u
A four-column theory for the origin of the triplet code: In a latest Biology Direct paper Paul G Higgs proposed .. http://tinyurl.com/d6wk6u