A Novel Theory on the Origin of the Genetic Code: A GNC-SNS Hypothesis |
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Authors: | Kenji Ikehara Yoko Omori Rieko Arai Akiko Hirose |
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Institution: | (1) Department of Chemistry, Faculty of Science, Nara Women's University, Kita-uoya-nishi-machi, Nara 630-8506, Japan, JP |
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Abstract: | We have previously proposed an SNS hypothesis on the origin of the genetic code (Ikehara and Yoshida 1998). The hypothesis
predicts that the universal genetic code originated from the SNS code composed of 16 codons and 10 amino acids (S and N mean
G or C and either of four bases, respectively). But, it must have been very difficult to create the SNS code at one stroke
in the beginning. Therefore, we searched for a simpler code than the SNS code, which could still encode water-soluble globular
proteins with appropriate three-dimensional structures at a high probability using four conditions for globular protein formation
(hydropathy, α-helix, β-sheet, and β-turn formations). Four amino acids (Gly G], Ala A], Asp D], and Val V]) encoded by
the GNC code satisfied the four structural conditions well, but other codes in rows and columns in the universal genetic code
table do not, except for the GNG code, a slightly modified form of the GNC code. Three three-amino acid systems (D], Leu
and Tyr; D], Tyr and Met; Glu, Pro and Ile) also satisfied the above four conditions. But, some amino acids in the three
systems are far more complex than those encoded by the GNC code. In addition, the amino acids in the three-amino acid systems
are scattered in the universal genetic code table. Thus, we concluded that the universal genetic code originated not from
a three-amino acid system but from a four-amino acid system, the GNC code encoding GADV]-proteins, as the most primitive
genetic code.
Received: 11 June 2001 / Accepted: 11 October 2001 |
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Keywords: | : Genetic code theories — SNS primeval genetic code — GNC primitive genetic code — Protein structure index — [GADV]-primitive protein — Genetic Code Evolution |
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