Exp Cell Res 1995 Mar 01;2171:57-64. doi: 10.1006/excr.1995.1063.

The mechanism of binding of exogenous DNA to sperm cells: factors controlling the DNA uptake.

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Mature sperm cells have the spontaneous capability of taking up exogenous DNA. Potential substrates for the interaction of the DNA with the sperm heads are specific classes of DNA-binding proteins. In the present work three major classes of DNA-binding proteins were identified by Southwestern analysis of sperm head protein extracts: a first class of about 50 kDa in molecular weight, a second one of 30-35 kDa, and finally a third one below 20 kDa. The latter group most probably contains sperm protamines. Our attention was particularly focused on the 30- to 35-kDa proteins as a substrate for DNA binding, as they represented the only group whose electrophoretic mobility was conserved among mammalian species. In addition they were the only class of DNA-binding proteins accessible to exogenous DNA in intact sperm cells. The purified 30- to 35-kDa proteins interacted in vitro with exogenous DNA and generated discrete protein/DNA complexes as determined by band shift assay. A factor blocking the binding of exogenous DNA to sperm cells was also identified in the seminal fluid of mammals and in echinoid spermatoza. The factor also exerted a powerful inhibitory effect on DNA uptake in sperm cells of heterologous species. The 30- to 35-kDa DNA-binding proteins appeared to be the specific target through which the inhibition was mediated. In the presence of the inhibitory factor, the 30- to 35-kDa lost the ability to bind exogenous DNA. Thus, the interaction of exogenous DNA with sperm cells does not appear to be a casual event but, on the contrary, relies on a molecular mechanism based on the cooperation of specific protein factors.

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Genes referenced: taf12