Mutational consequences of the evolution of mitochondrial genetic code

Abstract

Evolutionary process significantly reduced the size of human mitochondrial DNA (mtDNA). It also changed its genetic code from standard to mitochondrial. This study aimed to find evidence for the mutational effects of the evolution of mitochondrial genetic code. For this purpose R. americana mtDNA, which represents the ancestor mtDNA and still uses standard genetic code, was compared with human mtDNA. It was focused on 25 subunits of oxidative phosphorylation enzymes encoded by R. americana mtDNA and their mitochondrial and nuclear orthologs in humans. Human and R. americana mtDNAs were found similar in only one short region of COX3 gene. The similarity of R. americana mtDNA encoded genes with their human nuclear orthologs is ~6 fold higher than their mitochondrial orthologs. Protein similarity is significantly more conserved than DNA. Three conserved regions were discovered as the proofs of the mutational effect of mitochondrial genetic code evolution. The findings suggest that the evolution of mitochondrial genetic code can be one of the barriers in the horizontal transfer of remaining mtDNA encoded genes to nucleus. R. americana mtDNA can be used as a template for the allotopic expression of mitochondrial genes as a strategy toward the pathologies like aging and cancer.