Mitochondrial Dna from Protozoa1

is known from the extensive genetic studies made in yeast (EPHRUSSI 1958) I;nd Neurospora (WAGNER and MITCHELL 1955) that certain defects associated with mitochondrial proteins are inherited under the control of a cytoplasmic element. However, the chemical nature and the specific location of such an element in the cytoplasm have not yet been elucidated. In recent years, evidence has been accumulating that the mitochondrion contains deoxyribonucleic acid (DNA) and that this DNA might be capable of functioning in the synthesis of some proteins in the mitochondrion (LUCK and REICH 1964; and see NASS, NASS, and AFZELIUS 1965). Thus, it is likely that the DNA found in the mitochondrion (mitochondrial DNA) is indeed the vector of the cytoplasmic element, mutations of which may result in alteration of some mitochondrial proteins. Attractive as this possibility may be, there is no direct experimental evidence to prove this point. It was however felt that detailed quantitative as well as qualitative studies of the mitochondrial DNA might lead to the elucidation of the function that this DNA possibly implements within the mitochondrion. Furthermore, comparative studies of mitochondrial DNA particularly in related organisms are of special interest in light of the previous finding that the mean base compositions of DNA from related organisms are similar and thus the phylogenetic relations are reflected in DNA base composition (SUEOKA 1962; SCHILDKRAUT, MARMUR and DOTY 1962). I t was hoped that mitochondrial DNA also exhibits such a relationship. In this paper are reported the isolation and partial characterization of mitochondrial DNA’s from two related protozoa, Tetrahymena and Paramecium.