Cytoplasmic control of histone messenger RNA translation is not mediated through protein phosphorylation.

It was investigated whether the cytoplasmic control of histone synthesis, i.e. the selective and rapid degradation of histone mRNA following interruption of DNA replication, is linked to the phosphorylation of specific proteins of the translational apparatus or other cytoplasmic proteins. No specific protein phosphorylation was observed when synchronized HeLa cells in the S-phase were blocked with hydroxyurea or cytosine arabinoside and pulse-labeled simultaneously with [32P]orthophosphate. Protein phosphorylation was also studied in cell-free protein-synthesizing systems (S16 extracts) from blocked and unblocked S-phase cells under a variety of conditions. No protein could be detected that becomes specifically phosphorylated with [gamma-32P]ATP in a cell-free system derived from S-phase cells in which DNA replication and histone mRNA translation was interrupted with hydroxyurea.