The role played by exons in genomic DNA sequence correlations

The codon structure inside exons imposes a strong modulation with period-3 for genomic composition correlations. A new formalism for calculating nucleotide correlations along DNA sequences in terms of an irreducible set of six correlation functions is presented. New procedures to extract the corresponding period-3 modulations are also developed. These modulations are seen to be stronger for the irreducible self-correlation C_zz(k), which accounts only for the binding strength of dinucleotides (z stands for adenine or thymine minus cytosine or guanine concentrations). We investigate and model the relationship between exon distribution and genomic period-3 correlations for the D. melanogaster genome.