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. Sperm histone P2b ST2b 58 AGSYYSYRRRRCSPRRLYRLRRRRYRSSRRRRRRPCRRRRHRRVCRRVRRRRRCCRRR HSP3_HORSE Protamine 2b