FLUORESCENCE MICROSCOPY OF DNA-PROTEIN STRUCTURES FROM OSMOTICALLY LYSED MITOCHONDRIA OF YEAST AND TOBACCO

The mitochondrial nucleoid is a compact structure composed of DNA and protein. By fluorescence microscopy, decondensation of the nucleoids w as observed when yeast and tobacco mitochondria were osmotically lysed and subjected to an electric field. Structures stained with ethidium bromide were seen moving toward either the anode or the cathode. Since the movement of deproteinized DNA is toward the anode, the structures moving reward the cathode represent DNA-protein complexes with a net positive charge. Nucleoid decondensation and unfolding of the DNA prob ably resulted from the removal of weakly bound proteins; yet high-affi nity basic proteins were evidently retained yielding cationic DNA-prot ein structures. Some of the positively charged structures were observe d to break, presumably at single-stranded DNA regions, releasing negat ively charged particles. The DNA-protein structures ar er than the uni t genome, suggest ing that multigenomic, concatemeric DNA is present w ithin the mitochondria.