Protamines, in the footsteps of linker histone evolution

It was perhaps a lucky coincidence that the early attempts to establish the chemical composition of the cell nucleus were initially carried out on such diverse biological systems as salmon sperm heads (1) and geese and chicken erythrocytes (2). Examination of sperm and erythrocyte systems, respectively, lead to the protamine and histone concepts (3). We know with certainty that, with the exception of the male gametes, all somatic cells exclusively contain histones. Hence, in metazoans, protamines (4, 5) are confined to the sperm nuclear chromatin, and even among sperm, protamines are not always present. Indeed, a large number of metazoans contain somatic-like histones in their sperm, and some crustaceans (order Decapoda) lack any chromosomal pro-teins in their sperm (6, 7). Therefore, in contrast to the somatic nucleus, sperm chromatin may have a much more diverse protein composition. It was not until the first attempt of classification of the sperm nuclear basic proteins (SNBPs)2 by David Bloch (6, 8), an effort later on extended by Harold Kasinsky (7), that a clearer picture started to emerge in this regard