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5-hydroxymethylcytosine (5hmC) accumulates in transcribed gene regions (called ‘gene bodies’) and near enhancers, but its biological role has remained mysterious. A new study demonstrates that 5hmC serves to counteract inappropriate, spurious intragenic transcription in airway smooth muscle cells and by doing so, this DNA base functions in the prevention of chronic inflammation in the lung and an asthma-like phenotype.
