Abstract
Mitochondrial DNA molecules are packed into the 3-dimentionally organized structure, called mitochondrial-nucleoid. The function of mitochondrial genome must be conducted properly in this highly condensed structure. However, the mode of organization of mitochondrial DNA into nucleoid is largely unknown. When mitochondrial-nucleoids isolated from BY-2 cultured tobacco cells were treated with micrococcal nuclease (MNase) and their DNA was subjected to agarose-gel electrophoresis, DNA ladder was observed, suggesting that nucleosome-like repeated structure was present in the mitochondrial-nucleoid. MNase digests with minimum size (ca. 75 bp) purified through sucrose gradient centrifugal fractionation contained several kinds of proteins distinct from histones. This result suggests that the nucleosome-like repeated structures in mitochondrial-nucleoid are constructed by original proteins different from those present in cell-nuclear chromatin. Electromicroscopic observation of the fine structures of isolated and MNase-treated mitochondrial-nucleoids, is now on progress.
