The bovine mitochondrial endonuclease prefers a conserved sequence in the displacement loop region of mitochondrial DNA

The purified endonuclease of bovine heart mitochondria shows a remarkable preference for a specific site in bovine mtDNA. This site was identified using a recombinant DNA template which includes a 4.9-kilobase portion of the 16-kilobase bovine mitochondrial sequence encompassing all of the displacement loop region. The endonucleolytic target corresponds to an evolutionarily conserved sequence tract of 12 consecutive guanine residues that is found in an otherwise highly divergent domain of the mitochondrial displacement loop region. The preference for this site is several hundred-fold greater than other less favored sites. Unlike other less prominent cleavage loci, the conserved sequence tract is readily nicked in either or both DNA strands, even at 0 degrees C. These findings suggest that there is a specific interaction of the endonuclease with this site in vivo that may be important for mtDNA replication.