Codon distributions in DNA sequence of Escherichia coli

The distributions of codons in the DNA sequence of Escherichia coli K-12 are studied by using several statistical methods of analysis. Codons corresponding to the arnino acids leucine, alanine and isoleucine are considered. The pair distributions of the codons as a function of the pair separation are evaluated and are seen to decay exponentially. The exponential decay constants have a linear relation with the numbers of the codons, indicating that the codons are randomly distributed in the sequence. The pair correlation and power spectral methods also show similar statistical behavior of codons in the sequence, with the exception that there appear very small peaks about the frequency f = 0.286 in the power spectra of the amino acids leucine, alanine and isoleucine. Such a frequency reflects a periodicity of about 3.5 amino acids and a general helical structure of the proteins of the bacterium.