Intragenic rearrangements in the mitochondrial NADH dehydrogenase subunit 6 gene of vertebrates

The mitochondrial-encoded NADH dehydrogenase subunit 6 gene from 19 species of birds was sequenced. Comparison of the derived amino acid sequences in 22 avian species, six mammals, and two fishes, reveals an intragenic rearrangement in mammals. The C-terminal half of the mammalian protein includes an internal insertion of 10-15 amino acids and a C-terminal deletion of 8-9 amino acids. Based on comparative sequence alignments and hydropathy profile analysis, five hydrophobic segments (designated 1 to 5) corresponding to transmembrane regions are proposed. In this structural model of NADH dehydrogenase subunit 6, the mammalian insertion is found in a variable loop region between transmembrane segments 4 and 5.