Protamines from liverwort are produced by posttranslational cleavage and C-terminal di-aminopropanelation of several male germ-specific H1 histones.

Protamines are small, highly specialized, arginine-rich, intrinsically disordered chromosomal proteins that replace histones during spermiogenesis in many organisms. Previous evidence supports the notion that, in the animal kingdom, these proteins have evolved from a primitive replication-independent histone H1 involved in terminal cell differentiation. Nevertheless, a direct connection between the two families of chromatin proteins is missing. Here, we primarily used electron transfer dissociation (ETD) mass MS-based analyses, revealing that the protamines in the sperm of the liverwort Marchantia polymorpha result from post-translational cleavage of three precursor H1 histones. Moreover, we show that the mature protamines are further post-translationally modified by di-aminopropanelation, and previous studies have reported that they condense sperm chromatin through a process consisting of liquid phase assembly likely involving spinodal decomposition. Taken together, our results reveal that the interesting evolutionary ancestry of protamines begins with histone H1 in both the animal and plant kingdoms.