On the Nature of Chromosome-sized DNA Molecules

To learn how eukaryotic DNA is organized, we have been studying its structure. Our work has been devoted primarily to the question of whether a single DNA molecule runs the entire length of a chromosome. To answer this question, we have been measuring the size of the largest DNA molecules in gentle lysates of Drosophila cells by means of a special viscoelastic technique (Chapman et al., 1969). Here we will review published results (Kavenoff and Zimm, 1973) which provide evidence that there are DNA molecules which run the entire length of a chromosome and then we will consider the extent of our knowledge of such molecules and, for comparison, the structure of the genome of some diplornaviruses.