Comparative Analysis Of The Complete Mitochondrial Genomes Sequences Of Asio Flammeus And Asio Otus

Abstract: In this paper, two avian complete mitochondrial genomes of Strigifoxmes were sequenced and analyzed. The structure, evolution and function of control regions of avian mtDNA were also discussed.The complete mitochondrial genomes of Asio flammeus and Asio otus were sequenced and found to span 18,858 bp and 18,493 bp, respectively. It is surprising to find the former to be the largest among all avian mitochondrial genomes sequenced so far. The two genomes have very similar gene order with that of Gallus gallus, neither contains the pseudo control region, but both have a single extra base, namely Cytidine, at position 174 in ND3 gene. The nucleotide contents are obviously AT biased. The lengths of intergenic spacers and overlap genes, as well as the start codon and stop codon usage in the two owls are special in some species. The control regions of Asio flammeus and Asio otus' mitochondrial genomes span 3288 bp and 2926 bp respectively, which are the longest among vertebrates except for Myxine glutinosa and contribute to the large size of two genomes.The base composition and organization of control region of Asio flammeus and Asio otus are the same as the other reported birds. Based on the differential frequencies of base substitutions, the mitochondrial control region may be divided into three domains: domain Ⅰ —Ⅲ. Compared with other birds, most of the variations within the control region are clustered within domains I and HI, while domain II is conserved. Some conserved sequence motifs are also found in all three domains of control region of the two owls. The 3' end of control region of the two owls contains many repeated sequences. In Asio flammeus, the repeated sequences consisted of a 126 bp sequence repeated seven times and a 78 bp sequence repeated 14 times. There are 99 bp spacers between the two sets of repeats. The control region of Asio otus has also been found to contain two sets of repeats: a 127 bp sequence repeated eight times and a 78 bp sequence repeated seven times, with 55 bp spacers between the two sets of repeats. It is clear that the corresponding repeated units of the twoowls have high homology, which implies that they may have a common origin. In this study, we found that the repeated sequences are highly similar to a putative control element, i.e. Mt5, and may form stable stem-loop secondary structures. At present, replication slippage, the dominant mechanism, has been proposed to account for the origin of tandem repeat. Therefore, tandemly repeated sequences in the mtDNA control region are more likely to be generated in the regions where the polymerase activity is disrupted. Repeated sequences have been generally considered as redundancy in mtDNA. In this study, however, we found that such repeated sequences probably play an important role in regulating transcription and replication of mitochondrial genome. Acquisition of such ability has consequently improved selection advantage of species above during evolution. Our results may provide important clues for uncovering the origin and evolution mechanisms of mitochondrion genome.