Comparative analysis of mitochondrial fragments transferred to the nucleus in vertebrate

Mitochondrial DNA sequences transferred to the nucleus give rise to the socalled nuclear mitochondrial DNA (numt). In the GenBank database, 244 numts have been found in six orders of birds (Anseriformes, Columbiformes, Falconiformes, Charadriiformes, Galliformes and Passeriformes). Sequences alignment (NCBI-BLASTN) was carried out with mitochondrial and corresponding nuclear genome sequences in nine vertebrate species. The sequences with high homology were considered as numts. The number of numts ranged from 15 in chicken to 159 in chimpanzee. The sequences of numts in macaque, chimpanzee, and human spanned 100% of the entire mammalian mitochondrial genome. The reconstructed frequency of the mitochondrial gene transferred to the nucleus demonstrated that the rRNA genes had high frequencies than other mitochondrial genes. Using the RepeatMasker program, the transposable elements were detected in the flanking regions of each numt. The results showed that less than 5% of the flanking sequences were made up of repetitive elements in chicken. The GC content of 5'- and 3'-flanking regions of numts in nine species was less than 44%. The analysis of the flanking sequences provided a valuable understanding for future study on mechanism of mitochondrial gene transfer to the nucleus and the site of numt integration.