Separation and characterization of a satellite DNA from a yeast cytoplasmic “petite” mutant

Abstract

DNA prepared from the particular cytoplasmic “petite” mutant of Saccharomyces cerevisiae investigated in this work shows, when centrifuged in a caesium chloride density-gradient, two bands: a main band having the same density (ϱ = 1.700 g/cm 3) as nuclear DNA from wild-type cells, and also showing a heavier shoulder; and a satellite band which has a much lower density (ϱ = 1.672 g/cm 3) than mitochondrial DNA from wild-type cells (ϱ = 1.685 g/cm 3). The light satellite DNA has been isolated using hydroxyapatite column chromatography, a method which is also effective for isolating mitochondrial DNA from the wild-type cell DNA. Enzymic digestion of the light satellite DNA to nucleo-sides, and analysis of these on polyacrylamide gel columns have shown that it is formed by A and T in equimolar amounts, to the extent of 96%; G and C form only about 4% of the digest. When examined by electron microscopy, the light satellite DNA shows both linear and circular molecules, in contrast with nuclear DNA which shows only linear molecules. Chromatography of total DNA from both wild-type cells and the cytoplasmic petite mutant has also revealed the presence of a small nucleic acid component which is extremely rich in guanine; its origin is still unknown.