Phosphorylation of Chromosomal Basic Proteins in Maturing Trout Testis

During the replacement of histones by protamine at the terminal stages of trout spermatogenesis, both classes of chromosomal basic proteins are phosphorylated. Phosphorylation of newly synthesized protamine occurs in the cytoplasm. Newly synthesized phosphoprotamine is then transported into the nucleus and binds to DNA without appreciable dephosphorylation. Although the complex of phosphorylated protamine with DNA is as compact as the dephosphoprotamine-DNA complex, the affinity of protamine for DNA is decreased by phosphorylation. In contrast, pre-formed rather than newly synthesized histones are phosphorylated. The binding of histones to DNA as judged by salt or detergent dissociation does not appear to be significantly changed by phosphorylation.