Protamine-histone exchange

This protamine-histone exchange could provide a window of opportunity for maternally derived transcription factors to gain access to their c -cognate... 

Shortly after pronucleus formation and entry into S phase, transcription initiates in both pronuclei of the one-cell embryo (Figure 6). The male pronucleus supports higher levels of transcription than the female pronucleus, and this difference is attributed to their differences in chromatin structure that reflects their different histories (e.g., the protamine-histone exchange that occurs in the male pronucleus affords an opportunity for the sequestration of maternal transcription factors that is not available to the female pronucleus whose DNA is already packaged into chromatin). The first... 

At the terminal stage of spermatogenesis of salmon fish, nucleohistones are replaced by nucleoprotamine. Not much is known about the mechanisms by which one kind of basic polypeptide is replaced by another. What seems certain is that protamines are made in the cytoplasm and transferred to the nucleus before the displacement can take place. Prior to the exchange, both types of basic proteins, preformed histones and newly synthesized protamines, are phosphorylated. 

The role that phosphorylation plays in the exchange is not clear. Phosphorylation does not seem to modify the affinity of histones for DNA but slightly decreases the affinity of protamines for DNA [64]. 

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