The evolution of species-type specificity in the global DNA sequence organization of mitochondrial genomes

Prokaryote genomes and nuclear genomes of eukaryotes have a global DNA sequence organization that is species type specific, determined primarily by nearest-neighbor nucleotide associations, and independent of gene function and sequence length. The determinants of such a global structure have remained largely uncharacterized. The monophyletic and endosymbiotic origin of mitochondria permit examination of the influence of evolutionary time and host species type. Different global structures were seen among (i) protozoan and plant, (ii) fungal, (iii) algal (iv) nematode, (v) echinoderm, (vi) insect, and (vii) vertebrate species following examination of 28 complete mitochondrial genomes using chaos representation and measures of short-sequence representation. The mitochondrial genomes have biases in single-nucleotide and dinucleotide representation, specifically, an overrepresentation of A and T nucleotides and CC/GG and AG/CT dinucleotides and a deficiency of CG dinucleotides, in all but one genome. Dinucleotide representation is similar among (i) mitochondrial genomes of more closely related species; (ii) mitochondrial genomes and the Mycoplasma capricolum genome, a proposed progenitor of mitochondrial genomes; and (iii) mitochondrial genomes of diverse species, more so than between the mitochondrial and the nuclear genome of the same or a closely related species. It is hypothesized that sufficient evolutionary time has permitted host-specific constraints to affect nuclear and mitochondrial genomes and that different species type specific constraints influence nuclear and mitochondrial genome global structure.Key words: chaos representation, mitochondrial genomes, primary sequence organization, oligonucleotide frequencies.