Mitochondrial DNA
Mitochondrial DNA was discovered in the 1960s by Margit M. K. Nass and Sylvan Nass by electron microscopy as DNase-sensitive threads inside mitochondria, and by Ellen Haslbrunner, Hans Tuppy and Gottfried Schatz by biochemical assays on highly purified mitochondrial fractions.
Matthew Meselson
In the famous Meselson–Stahl experiment of 1958 he and Frank Stahl demonstrated through nitrogen isotope labeling that DNA is replicated semi-conservatively. In addition, Meselson, François Jacob, and Sydney Brenner discovered the existence of messenger RNA in 1961. Meselson has investigated DNA repair in cells and how cells recognize and destroy foreign DNA, and, with Werner Arber, was responsible for the discovery of restriction enzymes.