Ten-eleven-translocation (TET) dioxygenases
catalyze the oxidation of 5-methylcytosine (5mC), the central
epigenetic regulator of mammalian DNA. This activity dy-
namically reshapes epigenome and transcriptome by deposit-
ing oxidized 5mC derivatives, and initiating active DNA de-
methylation. However, studying this dynamic is hampered by
the inability to selectively activate individual TETs with tem-
poral control in cells. We report activation of TETs in mam-
malian cells by incorporation of genetically encoded 4,5-
dimethoxy-2-nitrobenzyl-L-serine as transient active site
block, and its subsequent deprotection with light. Our ap-
proach enables precise insights into the impact of cancer-
associated TET2 mutations on the kinetics of TET2 catalysis
in vivo, and allows time-resolved monitoring of target gene
activation and transcriptome reorganization. This sets a basis
for dissecting the order and kinetics of chromatin-associated
events triggered by TET catalysis, ranging from DNA de-
methylation to chromatin and transcription regulation
