PRM3 (protamine 3) is a small acidic protein expressed during spermatogenesis that plays a role in sperm function. Unlike the canonical protamines PRM1 and PRM2, which condense sperm DNA through histone substitution, PRM3 has a distinctive acidic character and cytoplasmic localization in elongated spermatids rather than nuclear localization 1. The Prm3 gene is an intronless member of the protamine gene cluster present across mammals, with mRNA first detected in early round spermatids and protein expression delayed until late spermatids 12. Functionally, PRM3 regulates sperm motility; male mice with Prm3 gene disruption exhibited reduced sperm motility compared to wild-type controls 1. However, this motility reduction did not significantly impair fertility in standard one-to-one mating tests, though competitive mating experiments suggested PRM3 contributes to male reproductive success 1. The developmental timing of PRM3 expression parallels other spermatogenic proteins, with translation of Prm3 mRNA developmentally delayed similar to Prm1, Prm2, and Tnp2 1. PRM3's specific role in flagellar function and sperm motility distinguishes it functionally from other protamines focused on chr16 condensation.