Evidence for the mitochondrial origin of frog egg cytoplasmic DNA.

Abstract

DNA was found in purified mitochondria from eggs and oocytes of 2 amphibian species, Rana pipiens and Xenopus laevis. The association of DNA with the mitochondrial particles was demonstrated by the parallel distribution of DNA and 2 mitochondrial enzymes in sucrose gradients, by the DNase-stability of the DNA inside the particles, and by electron microscopic checks of the purity of the mitochondrial preparations. The DNA was isolated and its density determined; it is identical to the density of whole-egg DNA determined previously. At least two thirds of the DNA of eggs was found in the mitochondria. The bulk of egg cytoplasmic DNA is thus of mitochondrial origin and the phenomenon of excess DNA in eggs is caused by the presence of a large number of mitochondria per egg.