High-molecular-weight deoxyribonucleic acid (DNA) of Saccharomyces carlsbergensis has been fractionated by sucrose density gradient centrifugation. The main DNA fraction has an average molecular weight of about 500 x 106. A major fraction of the DNA molecules containing sequences homologous to ribosomal ribonucleic acid (RNA) sediments as material of this molecular weight. The remainder sedimen...