Abstract
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/cm 3, 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.
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