ApA dinucleotide periodicity in prokaryote, eukaryote, and organelle genomes

Computer analyses of various genome sequences revealed the existence of certain periodical patterns of adenine-adenine dinucleotides (ApA). For each genome sequence of 13 eubacteria, 3 archaebacteria, 10 eukaryotes, 60 mitochondria, and 9 chloroplasts, we counted frequencies of ApA dinucleotides at each downstream position within 50 bp from every ApA. We found that the complete genomes of all three archaebacteria have clear ApA periodicities of about 10 bps. On the other hand, all of the 13 eubacteria we analyzed were found to have an ApA periodicity of about 11 bp. Similar periodicities exist in the 10 eukaryotes, although higher organisms such as primates tend to have weaker periodic patterns. None of the mitochondria and chloroplasts we analyzed showed an evident periodic pattern.