GNC hypothesis or GNC-SNS primeval genetic code hypothesis refers to a hypothesis about the origin of genes. While almost all of the organisms on present Earth shares the universal genetic code, in GNC hypothesis it is argued that two primeval genetic codes preceded the present genetic code as follows.
First, there emerged GNC primeval genetic codes involving 4 codons (GGC, GCC, GAC and GUC), which code 4 GADV-amino acids (glycine, alanine, aspartic acid and valine).
Second, GNC code evolved to SNS primeval genetic codes involving 16 codons (GGC, GGG, GCC, GCG, GAC, GAG, GUC, GUG, CUC, GUG, CCC, CCG, CAC, CAG, CGC and CGG), which code 10 amino acides (glycine, alanine, aspartic acid, valine, glutamic acid, leucine, proline, histidine, glutamine, arginine).
This hypothesis was first proposed by Kenji Ikehara at Nara Women's University.
GNC hypothesis is based on the following facts.
Proteins composed of GADV-amino acids coded by GNC primeval genetic code can form 4 fundamental structures found in proteins in present organisms, namely, hydrophobic and hydrophilic structures, α-helices, β-sheets, and turns (or coils).
Proteins composed of 10 amino acides coded by SNS primeval genetic code can form 6 fundamental structures, namely, hydrophobic and hydrophilic structures, α-helices, β-sheets, turns, acidic and basic fragments.
Ikehara, Kenji; Omori, Yoko; Arai, Rieko; Hirose, Akiko (2002). "A Novel Theory on the Origin of the Genetic Code: A GNC-SNS Hypothesis". Journal of Molecular Evolution. Springer-Verlag. 54: 530–538. doi:10.1007/s00239-001-0053-6.
