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Methylation of histone H3 at Lys 9 is causally linked to formation of heterochromatin and to long-term transcriptional repression. We report an unexpected pattern of H3 Lys 9 methylation occurring at a subset of inducible inflammatory genes. This pattern is characterized by relatively low constitutive levels of H3 Lys 9 methylation that are erased upon activation and restored concurrently with post-induction transcriptional repression. Changes in H3 Lys 9 methylation strongly correlate with RNA polymerase II recruitment and release. In particular, remethylation correlates with RNApolII release more strongly than does histone deacetylation. We propose that, by generating a window of time in which transcription is permitted, dynamic modulation of H3 Lys 9 methylation adds an additional regulatory level to transcriptional activation of tightly controlled inducible genes.
Saccani et al. (Sun,) studied this question.