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Sperm nuclear proteins were extracted and subsequently separated by acid-urea (AU) polyacrylamide gel electrophoresis. The relative histone (H2B) to protamine (P1+ P2) and protamine P1 to P2 ratios were estimated by densitometric analysis of the AU gels. lmmunoblotting experiments (using H2B, P1 and P2 antibodies) were conducted to confirm the specificity of the bands. The pattern and intensity of H2B staining in human spermatozoa was assessed by immunocytochemistry. Sperm samples from infertile men had a significantly higher proportion of histone H2B to protamine (P1+ P2) than did samples from fertile men (0.38 vs. 0.08, P< 0.001). Immunocytochemistry experiments demonstrated a punctuated staining pattern (with strong, intermediate or weak H2B staining intensity) throughout the sperm head. Infertile men had a higher proportion of spermatozoa exhibiting strong and …