Concordant evolution of coding and noncoding regions of DNA made possible by the universal rule of TA/CG deficiency-TG/CT excess.

The universal rule of TA/CG deficiency-TG/CT excess previously proposed as the construction principle of coding sequences applies to noncoding regions of the gene as well. Analysis of a 1989-base-long gene sequence for mouse immunoglobulin gamma 2a heavy-chain constant region as well as the 19,002-base-long gene sequence for human serum albumin revealed deficiency and overabundance of very similar sets of base trimers and tetramers in the coding and noncoding regions of the same gene, in spite of the fact that noncoding regions were considerably richer in A + T. Inasmuch as this universal rule does not discriminate one strand of DNA double helix from another, two complementary DNA strands of the entire gene maintained nearly perfect symmetry. That is to say, the degrees of excesses, deficiencies of the 64-base trimers remained nearly identical between two complementary strands, and this symmetry was only slightly disturbed in the coding region. It would thus appear that the universal rule as an intrinsic force has been exerting far greater influence than natural selection in the evolution of genes.