CLOCK leaves its mark on histones

Transcriptional regulation of circadian rhythms in mammals involves a negative-feedback loop whereby a CLOCK–BMAL1 complex activates transcription of the genes encoding the proteins PER1 (Period 1), PER2, CRY1 (Cryptochrome 1) and CRY2, which feed back to inhibit the activity of CLOCK–BMAL1. It is becoming evident that chromatin remodeling has a crucial role in the transcriptional regulation of genes governing circadian rhythms. This is highlighted in a recent report that shows that CLOCK has histone acetyltransferase activity, thus, demonstrating that molecular components of the biological clock can themselves catalyze chromatin modifications.