During mammalian spermiogenesis, histones are transiently replaced by several low molecular weight proteins called transition proteins (TNPs) . Transition proteins facilitate chromatin transformation from the nucleosome structure to the nucleoprotamine structure during spermatid differentiation . Transition protein-2, also known as TNP2, and TP2, maps to human chromosome 16p13.13 and encodes a highly basic nuclear protein. TNP2 is a spermatid-specific product of the haploid genome which replaces histone and is itself replaced in the mature sperm by the protamines . TNP2 is not a critical factor for shaping of the sperm nucleus, histone displacement, initiation of chromatin condensation, binding of protamines to DNA, or fertility . However, TNP2 is necessary for maintaining the normal processing of protamine 2 and, consequently, the completion of chromatin condensation. If TNP1 is missing, TNP2 may partially compensate for TNP1, but this dysregulation of nucleoprotein replacement results in an abnormal pattern of chromatin condensation and in reduced fertility .
Nuclear transition protein 2; TNP2; TP-2