Changes in the methylation pattern of core histones during heat-shock in Drosophila cells.

The post-translational methylation of histones in the presence of inhibitors of protein synthesis, was studied during a heat-shock to Drosophila cells in culture. In control cells (23 degrees C), both histones H3 and H4 are methylated. After heat-shock (37 degrees C), there is a dramatic reduction in the methylation of H3 and an increase in the methylation of another core histone identified as H2B. These changes in the pattern of methylation vary with the temperature of the heat-shock. The increased methylation of H2B is also observed in arsenite-treated cells but the methylation of H3 is unchanged, being similar to that observed in control cells. Inhibition of synthesis of heat-shock proteins has no effect on the methylation changes, suggesting that heat-shock proteins are not directly involved in the methylation reaction. These changes could be involved in the extensive transcriptional regulation occurring in these cells during heat-shock.