Originally published as Genetics Published Articles Ahead of Print on August 22, 2005.

Genetics, Vol. 171, 1695-1705, December 2005, Copyright © 2005
doi:10.1534/genetics.105.046243

Replication Origin of Mitochondrial DNA in Insects

Shigeru Saito1, Koichiro Tamura and Tadashi Aotsuka

Department of Biological Sciences, Tokyo Metropolitan University, Hachiouji, Tokyo 192-0397, Japan

1 Corresponding author: Laboratory of Bioscience, Department of Welfare Engineering, Faculty of Engineering, Iwate University, 4-3-5, Ueda, Morioka, Iwate 020-8551, Japan.
E-mail: shigeru{at}iwate-u.ac.jp

The precise position of the replication origin (OR) of mtDNA was determined for insect species belonging to four different orders (four species of Drosophila, Bombyx mori, Triborium castaneum, and Locusta migratoria, which belong to Diptera, Lepidoptera, Coleoptera, and Orthoptera, respectively). Since the free 5' ends of the DNA strands of mtDNA are interpreted as the OR, their positions were mapped at 1-nucleotide resolution within the A + T-rich region by using the ligation-mediated PCR method. In all species examined, the free 5' ends were found within a very narrow range of several nucleotides in the A + T-rich region. For four species of Drosophila, B. mori, and T. castaneum, which belong to holometabolous insects, although the OR's were located at different positions, they were located immediately downstream of a series of thymine nucleotides, the so-called T-stretch. These results strongly indicate that the T-stretch is involved in the recognition of the OR of mtDNA at least among holometabolous insects. For L. migratoria (hemimetabolous insect), on the other hand, none of the long stretches of T's was found in the upstream portion of the OR, suggesting that the regulatory sequences involved in the replication initiation process have changed through insect evolution.