Protamines substitute for histones in the chromatin of sperm during the haploid phase of spermatogenesis. They compact sperm DNA into a highly condensed, stable and inactive complex. Interacts with TDRP. Testis. Proteolytic processing into mature chains is required for histone eviction during spermatogenesis. Transition proteins (TNP1 and TNP2) are required for processing. Belongs to the protamine P2 family.