Studies on Mitochondrial Structure and Function in Physarum polycephalum. VII. Association between Mitochondrial Nuclear DNA and the Outer Limiting Membrane Complex

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Abstract
The spatial relationship between the mitochondrial nucleus (mt-nucleus) containing a large amount of DNA (mtDNA) and the mitochondrial limiting membrane in P. polycephalum was investigated. After labeling the mtDNA with [3H]-thymidine, significant labels appeared over the space of the mitochondrial matrix and the mt-nucleus; this suggested that an appreciable amount of the mtDNA exists in the matrix. When the cristae and inner limiting membrane were removed selectively by Triton X-100 lysis, DNA-like fibers appeared to extend from the mt-nucleus to the matrix space. One end of these fibers was attached to a knob-like structure that adhered to the outer limiting membrane of the mitochondrion. A portion of the mtDNA in the isolated mt-nucleus also extended from the mt-nucleus and was associated with mitochondrial membrane-like patches through the knob-like coupling. Apparently the mtDNA extends from the mt-nucleus throughout the mitochondrial matrix and is associated with the mitochondrial limiting membrane complex in the mitochondrion in situ.