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 (PubMed:28366643). Transition proteins (TNP1 and TNP2) are required for processing (PubMed:28366643). Male mice are sterile due to reduced compaction of chromatin in sperm. Belongs to the protamine P2 family.