Protamines substitute for histones in the chromatin of sperm during the haploid phase of spermatogenesis, and are the major DNA-binding proteins in the nucleus of sperm in many vertebrates. They package the sperm DNA into a highly condensed complex in a volume less than 5% of a somatic cell nucleus. Many mammalian species have only one protamine (protamine 1); however, a few species, including human and mouse, have two. This gene encodes protamine 2, which is cleaved to give rise to a family of protamine 2 peptides. Alternatively spliced transcript variants have also been found for this gene.