Mammalian mitochondrial DNA replicates bidirectionally from an initiation zone

Previous data from our laboratory suggested that replication of mammalian mitochondrial DNA initiates exclusively at or near to the formerly designated origin of heavy strand replication, O-H, and proceeds unidirectionally from that locus. New results obtained using two-dimensional agarose gel electrophoresis of replication intermediates demonstrate that replication of mitochondrial DNA initiates from multiple origins across a broad zone. After fork arrest near O-H, replication is restricted to one direction only. The initiation zone of bidirectional replication includes the genes for cytochrome b and NADH dehydrogenase subunits 5 and 6.