Histone mRNA metabolism during the mouse fibroblast cell cycle.

The synthesis of histone mRNA in the nucleus and the eventual appearance of histone mRNA in the cytoplasm of 3T6 Swiss mouse embryo fibroblasts was investigated with a highly labelled cDNA probe complementary to histone mRNA. Very low levels of histone mRNA were found in G1 phase nuclei, with even lower levels in the cytoplasm. At the onset of DNA synthesis, there is a rapid increase in histone mRNA synthesis, with a concomitant increase of histone mRNA in the cytoplasm followed by its decline in both nucleus and cytoplasm on entering the G2 phase of the cell cycle. The decline in the nucleus is much more rapid than in the cytoplasm.