J. Mrazek et J. Kypr, BIASED DISTRIBUTION OF ADENINE AND THYMINE IN GENE NUCLEOTIDE-SEQUENCES, Journal of molecular evolution, 39(5), 1994, pp. 439-447
We analyzed occurrences of bases in 20,352 introns, exons of 25,574 pr
otein-coding genes, and among the three codon positions in the protein
-coding sequences. The nucleotide sequences originated from the whole
spectrum of organisms from bacteria to primates. The analysis revealed
the following: (1) In most exons, adenine dominates over thymine. In
other words, adenine and thymine are distributed in an asymmetric way
between the exon and the complementary strand, and the coding sequence
is mostly located in the adenine-rich strand. (2) Thymine dominates o
ver adenine not only in the strand complementary to the exon but also
in introns. (3) A general bias is further revealed in the distribution
of adenine and thymine among the three codon positions in the exons,
where adenine dominates over thymine in the second and mainly the firs
t codon position while the reverse holds in the third codon position.
The product (A(1)/T-1) x (A(2)/T-2) x (T-3/A(3)) is smaller than one i
n only a few analyzed genes.