Phosphorylation of histone H3 correlates with transcriptionally active loci

Posttranslational modifications of the N-terminal tails of the core histone s within the nucleosome particle are thought to act as signals from the chr omatin to the cell for various processes. The experiments presented here sh ow that the acetylation of histones H3 and H4 in polytene chromosomes does not change during heat shock. In contrast, the global level of phosphorylat ed H3 decreased dramatically during a heat shock, with an observed increase in H3 phosphorylation at the heat shock loci. Additional experiments confi rm that this change in phosphorylated H3 distribution is dependent on funct ional heat shock transcription factor activity. These experiments suggest t hat H3 phosphorylation has an important role in the induction of transcript ion during the heat shock response.