On negative selection against ATG triplets near start codons in eukaryotic and prokaryotic genomes

The frequencies of ATG triplets in the genomes of various species were systematically analyzed, and the frequency of ATG triplets was significantly low around start codons in both prokaryotic and eukaryotic genomes. In eukaryotes, however, the frequency decrease before the start codon is much more evident than that after the start codon. In prokaryotes, on the other hand, the ATG frequency pattern around the start codon is less evident, and-more importantly-symmetric. We also computed average distances between a start codon and its nearest upstream-located ATG triplet and found a general tendency for the average distances to be longer in higher organisms.