In mammals, the protamines do not directly replace the histones. Instead, another group of basic proteins, the transition proteins, act as intermediaries in the histone-to-protamine transition ...

Until the advent of lente insulin the preparation of insulins with prolonged action had been achieved by the addition of basic protein substances such as the protamines, globins and histones ...

However, the sperm used must have the correct ratio of two proteins, protamines P1 and P2, to provide tight packing for sperm DNA. Otherwise DNA can fragment, leading to poor embryo quality.