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Protamines are small, arginine-rich, nuclear proteins that replace histones and transition proteins late in spermiogenesis. They play an important role in spermatid genome inactivation and sperm chromatin condensation and stabilization. Protamine binding to DNA may even contribute the forces that drive nuclear compaction and contribute to head shaping. DNA bound to protamines is much more densely packed than DNA packaged by histones, and the genes associated with protamine can only be expressed when the protamines are removed after fertilisation.  REVIEW ARTICLE ON PROTAMINES
A series of monoclonal antibodies were developed in the late 1980's at Lawrence Livermore National Laboratory by Drs. Rod Balhorn, Andrew Wyrobek and Larry Stanker as reagents for detecting and identifying the mammalian protamines P1 and P2. The natural human antigens were used to produce three antibodies that bind not only to the free proteins, but also to the protamines bound to DNA in the chromatin of spermatids and mature sperm. Two of the antibodies, the anti-protamine P1 antibody Hup 1N and the anti-protamine P2 antibody Hup 2B have been shown to bind to protamine molecules isolated from the sperm of a wide range of mammalian species.  The Hup 1M antibody is highly specific and recognizes only the human P1 protamine.
In the two decades following their development and characterization, these antibodies have been used by more than 100 investigators in the field of reproductive biology as tags for the two protein biomarkers that characterize spermatid maturation and sperm development in mammals. The antibodies have also been used to monitor the timing of protamine synthesis during spermiogenesis, identify cells expressing protamine transgenes, or visualize protamine P1, P2 or the P2 precursors by ELISA, and in Western blots or in immunograms following their separation and purification by HPLC (see REFERENCES).