Modification of Histones during Spermatogenesis in Trout

Trout testis cells were incubated with 13H]arginine and lysine and inorganic [32P]phosphate. Histones were extracted with acid and the major fractions (I, IIbl, IIb2, III monomer, and IV) were resolved by chromatography on BioGel P-10. The profile of 32P incorporation was time dependent. When the phosphorylated histones in each of the major fractions were resolved from unphosphorylated species by starch gel electrophoresis, about 40 to 50% of histone I, 15 to 20% of histone IIb,, 5% of histones IIbz and III, and 30 to 40% of histone IV was found to be phosphorylated. These different levels for each histone suggest that in each case phosphorylation may have a separate function other than, or in addition to, the usually postulated one of direct gene derepression. Histone IIbI is phosphorylated and dephosphorylated shortly after its synthesis, suggesting that phosphorylation and dephosphorylation of newly synthesized histone IIbl may play a role in its correct binding to DNA. This is in contrast to histone IV where acetylation and deacetylation may be important in its correct .binding to DNA.