The human spermatozoa genome. Analysis by DNA reassociation kinetics

The physicochemical characteristics of the human spermatozoa DNA have been analyzed by means of analytical ultracentrifugation and reassociation kinetics and compared with DNA from a somatic human cell, the leukocyte. Human spermatozoa DNA is composed of a major (86.7%) and a minor (13.3%) component with buoyant densities in neutral CsCl corresponding to 1.697 and 1.704 g/cm3, respectively. The DNA obtained from leukocytes contained only the first component. Reassociation kinetics of sheared DNA showed that the most rapidly-renatured repeated sequences consituted 12.1% of the sperm genome and only 9.2% of leukocyte genome. On the contrary single copy sequences were more abundant in leukocyte (64%) than in spermatozoa (59%) DNA. Reassociation kinetics with long DNA fragments (2000 nucleotides) were clearly different between sperm and leukocyte DNA, indicating the presence in sperm cells of a specific cluster of highly repetitive DNA. This entity may play a role in giving the spermatozoa nucleus its characteristic properties, involving supercoiling, quasi crystal structure, stability, lack of transcription, etc. and secondarily may function as an early pairing mechanism during syngamy.