Abstract
Mitochondrial-nucleus (nucleoid) is defined as a DNA-protein complex of mitochondria. Mitochondrial DNA molecules are packed into highly condensed structure, while the genome function must be conducted properly in the structure. However, mechanism of organization of mitochondrial DNA was almost unknown. When mitochondrial-nuclei isolated from BY-2 cultured tobacco cells were treated with micrococcal nuclease (MNase) and their DNA was subjected to agarose-gel electrophoresis, DNA ladder (minimum size was ~75 bp) was observed, suggesting that nucleosome-like structure was present in mitochondrial-nucleus. The DNA ladder did not observed when isolated mitochondrial-nuclei were pretreated with proteinase K or NaCl (≥ 1 M) before treatment with MNase, suggesting that mitochondrial DNA was protected by the proteins that bound DNA through electrostatic interaction. Further experiments, such as electromicroscopic observation of the fine structures of isolated and MNase-treated mitochondrial-nucleus, are now on progress.
