- Ikehara K. Degeneracy of the genetic code has played an important role in evolution of organisms. SOJ Genet Sci; 3: 1-3 (2016).
- Ikehara K. “GADV hypothesis on the origin of life –Life emerged in this way-” LAP LAMBERT Academic Publishing, Saarbrucken, Germany (2016).
- Ikehara, K. Evolutionary Steps in the Emergence of Life Deduced from the Bottom-Up Approach and GADV Hypothesis (Top-Down Approach). Life (Basel), 6, 6 (2016).
- Ikehara, K. Evolutionary steps in the emergence of life have come into view. Atlas of Science, May 1 (2016).
- Ikehara K. [GADV]-protein world hypothesis on the origin of life. Orig. Life Evol. Biosph., 44, 299–302 (2014).
- Ikehara, K. Protein ordered sequences are formed by random joining of amino acids in protein 0th-order structure, followed by evolutionary process. Orig. Life Evol. Biosph., 44, 279–281 (2014).
- [GADV]-Protein World Hypothesis on the Origin of Life. Kenji Ikehara,“Genesis: In the Beginning: Precursors of Life, Chemical Models and Early Biological Evolution”. Seckbach, J. (ed.), Springer, 107-122 (2012).
- Kenji Ikehara, “Origin of the Genetic Code and Genetic Disorders”(“Advances in the Study of Genetic Disorders”, K. Ikehara, Ed.) InTech-Open Access Publisher (November, 2011)
- Pseudo-replication of [GADV]-proteins and Origin of Life, Kenji Ikehara, Int. J. Mol. Sci., (International Journal of Molecular Sciences) Vol. 10, No. 4, 1525-1537 (2009)
- Kenji Ikehara, GNC-SNS Hypothesis of the Origin and Evolution of the Genetic Code. As a Chapter 4.06 in “Proncipia Bi®o-informatica” by J.C.Biro (2009).
- Origin and Evolutionary Process of the Genetic Code. Kenji Ikehara and Yuka Niihara, Current Medicinal Chemistry (CMC) Vol. 14, No. 30, 3221-3231 (2007).
- Catalytic Activities of [GADV]-Peptides: Formation and establishment of [GADV]-protein world for the emergence of life. Takae Oba, Jun Fukushima, Masako Maruyama, Ryoko Iwamoto and Kenji Ikehara, Olig. Life Evol. Biosph., Vol. 35, No. 5, 447-460 (2005).
- Possible Steps to the Emergence of Life: The [GADV]-Protein World Hypothesis. Kenji Ikehara, The Chemical Record, Vol. 5, Issue 2, 107-118 (2005).
- A Novel Theory on the Origin of the Genetic Code: A GNC-SNS Hypothesis. Kenji Ikehara, Yoko Omori, Rieko Arai and Akiko Hirose, J. Mol. Evol., Vol. 54, 530-538 (2002).
- Origins of Gene, Genetic Code, Protein and Life: comprehensive view of life systems from a GNC-SNS primitive genetic code hypothesis (a modified English version of the paper appeared in Viva Origino, Vol. 29, 66-85 (2001)) Kenji Ikehara, J. Biosci., Vol. 27, 165-186 (2002).
- A Possible Origin of Newly-Born Bacterial Genes: Significance of GC-rich nonstop frame on antisense strand. Kenji Ikehara, Fumiko Amada, Shigeko Yoshida, Yuji Mikata and Akira Tanaka, Nucl. Acids Res., Vol. 24, 4249-4255 (1996).
- Unusually Biased Nucleotide Sequences on Sense Strands of Flavobacterium sp. Genes Produce Nonstop Frames on the Corresponding Antisense Strands. Kenji Ikehara, and Eriko Okazawa, Nucleic Acids Res., Vol. 21, No. 9, 2193-2199 (1993).
In G & L Kyosei Institute
KEIHANNA Lab Wing, 4th Floor
1-7 Hikaridai, Seika-cho, Souraku-gun, Kyoto Prefecture, Japan
1972 – 1978 University of Tokyo, Faculty of Sciences, Department of Biochemistry and Biophysics, Research Associate
1978 -1989 Nara Women’s University, Faculty of Science, Department of Chemistry, Associate Professor
1989 – 2008 Nara Women’s University, Faculty of Science, Department of Chemistry, Professor
2006 – 2008 Nara Women’s University, Faculty of Science, Dean
2008 – 2010 Narasaho College Lifelong Education Center, Director
2010 – 2015 Open University of Japan, Nara Study Center, Director
2015 – Present GADV Laboratory, Head, in G & L Kyosei Institute, Head
Discussion on protein structure formation usually begins with the primary structure or amino acid sequence of the protein, not with amino acid composition. Although we happened to use amino acid composition for investigation of protein structure formability, it resulted in interesting conclusions, as described below.
Structure formability is the same for any protein of the same amino acid composition, that was randomly selected for assembling. This means that every protein synthesized by random peptide bond formation among amino acids in the amino acid composition could be folded into similar but into different structures. Proteins can have the same amino acid composition but different sequences. We call such a specific amino acid composition that is favorable for protein structure formation “protein 0th-order structure”.
Since the genetic code occupies a core position connecting genetic function with catalytic function in the fundamental life system, the origin and evolution of the genetic code is quite important for understanding formation process of the fundamental life system composed of gene, genetic code and protein. In facts, GNC-SNS primitive genetic code hypothesis gave an opportunity for proposing [GADV]-protein world hypothesis (GADV hypothesis) on the origin of life.
The GNC-SNS primitive genetic code hypothesis assumes that the universal genetic code or standard genetic code originated from GNC primeval genetic code encoding the respective [GADV]-amino acids with four codons through SNS primitive genetic code, which codes for 10 amino acids with sixteen codons. According to the hypothesis, it is considered that the both substantially and formally triplet genetic code evolved from substantially singlet but formally triplet GNC code through substantially doublet but formally triplet SNS code.
I started from a study on the entirely new ancestor genes, i.e. the first ancestor genes in gene families consisting of homologous genes. From analyses of microbial genes and proteins obtained from the GenomeNet Database, I found that the first ancestor genes could be produced from non-stop frames on anti-sense strands of, not AT-rich, but GC-rich microbial genes [GC-NSF(a)].
This conclusion was mainly based on the facts that hypothetical proteins encoded by GC-NSF(a)s satisfied six conditions for folding of polypeptide chains into water-soluble globular proteins (hydropathy, α-helix, β-sheet and turn/coil structure formations, acidic amino acid and basic amino acid compositions) and that the probability of stop codon appearance is sufficiently small to produce non-stop frames on the GC-NSF(a)s.
The six conditions were obtained by examining the average values of extant proteins plus/minus standard deviations. Those average values of most proteins held nearly-constant levels, regardless of GC contents, which were obtained by calculation using amino acid structural indexes and amino acid compositions of currently observed microbial proteins encoded by seven microbial genomes with different GC contents.