RESUMEN
Xenopus laevis spermatozoa and mouse epididymal spermatozoa were compared in their ability to bind plasmid DNA. Spermatozoa of both species are endowed with a very similar binding capacity for plasmid pAPrC DNA carrying the complete Rous sarcoma virus (RSV) DNA. Our experiments failed to detect any substantial differences between both types of sperm cells in the kinetics of DNA binding, maximum DNA binding capacity, effect of various ions, metabolic inhibitors and substrates on DNA binding, etc. Each X. laevis and mouse sperm cell associates, on an average, with about 50 and 45 molecules, respectively, of the plasmid DNA in a DNase resistant form, if spermatozoa were exposed to the DNA at a concentration of 0.5 microgram/5 x 10(6) sperm cells. The uptake of the DNA by both types of sperm cells is strongly inhibited by heparin. The 37-kDa factor IF-1 shown by Zani et al. (1995) to specifically block DNA binding to mouse sperm cells inhibited the interaction between pAPrC DNA and frog spermatozoa with a similar intensity.
