The modifications in the methylation patterns of H2B and H3 after heat shock can be correlated with the inactivation of normal gene expression.

The potential significance of the important post-synthetic methylation changes of core histones observed upon heat shock or after an arsenite treatment has been studied in Drosophila Kc cells. The changes in the histone methylation patterns appeared to be linked with the repression of normal gene expression rather than with the activation of the heat shock genes. Thus following a brief heat shock, the kinetics of recovery of the normal pattern of gene expression could be correlated with those of the return to a normal pattern of methylation of histones H2B and H3. Experiments with different inducers and a transcriptional inhibitor also suggest that the decreased methylation of H3 and the increase in that of H2B are an effect of the repression of transcription processes.