Sequence homologies among mitochondrial DNA-coded URF2, URF4 and URF5.

Amino acid sequences coded for by 13 different genes of mammalian mitochondrial DNA (mtDNA) including 8 unassigned open reading frames (URFs) were compared in pairs. It was found that significant homologies exist among the amino acid sequences of the three URFs (URF2, URF4 and URF5) with a probability of occurrence of less than 10(-5). This result strongly suggests that the 3 URFs evolved from a single ancestral gene by a series of gene duplications. A phylogenetic tree based on the alignment of the URF sequences from mammals, an insect, a fungus and protozoa revealed a very remote divergence of the 3 URFs, going back to a time before separations of animal/protozoa and animal/fungus.