Deoxyribonucleic acid loop domain tertiary structure in mammalian spermatozoa.

In the four decades since the discovery of the basic structure of the DNA double helix, researchers have been investigating the more dynamic tertiary structures that DNA assumes in the various forms of chromatin. The tertiary structure of DNA is important because it is directly related to the function of the genome: for the cell to access the information that is present in the genome accurately and efficiently, the DNA must be in an organized form. This paper reviews the recent work on one particular enigmatic structural form of eukaryotic DNA, that of the highly condensed spermatozoa. Based on the literature and on recently completed experiments in the field, a new model for DNA packaging in sperm nuclei is presented. In this model, each individual DNA loop domain in the sperm chromatin is condensed into a toroid-shaped structure termed the DNA loop doughnut.