Statistical Analysis of Codon Pairs Usage in Prokaryotic Genomes


  • Ivan Ivanov
  • Kiril Kirilov Roumen Tsanev Institute of Molecular Biology-Bulgarian Academy of Sciences



Genetic information is coded by the collinear arrangement of four nitrogen bases - adenine (A), guanine (G), cytosine (C) and thymine/uracil (T/U) along with the polynucleotide chains of DNA and RNA. They are combined in triplets called odons. Each of the 64 codons, except for UAA, UAG and UGA, codes for one (out of twenty) amino acids . The genetic information is translated/decoded by the help of transfer RNAs (tRNAs). The latter bear complementary triplets, called anticodons and also a single covalently bound amino acid. The place of decoding is the ribosome. It contains two sites (A and P) for binding of tRNAs. Therefore the accommodation of two tRNAs, each carrying one amino acid, in these sites is a prerequisite for the sequential formation of dipeptide, tripeptide and polypeptide (protein) products. At every moment of translation the two tRNAs in the A and P ribosomal sites are selected on the basis of the two translating codons in mRNA attached to the same ribosome.