Chromatin remodeling during spermiogenesis: a possible role for the transition proteins in DNA strand break repair.

An important chromatin remodeling process is taking place during spermiogenesis in mammals and DNA strand breaks must be produced to allow the accompanying change in DNA topology. Endogenous DNA strand breaks are indeed detected at mid-spermiogenesis steps but are no longer present in mature sperm. Both in vitro and in vivo evidence suggests that the DNA-binding and condensing activities of a set of basic nuclear "transition proteins" may be crucial to the integrity of the chromatin remodeling process. We propose that these proteins are necessary for the repair of the strand breaks so that DNA fragmentation is minimized in the mature sperm.