Turning Off Transcription with Bacterial RNA Polymerase through CuAAC Click Reactions of DNA Containing 5‐Ethynyluracil

Copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) click reaction in the major groove of DNA containing 5‐ethynyluracil ( U E ) with azides was used for turning off sequence‐specific protein–DNA interactions. The concept was first demonstrated on switching off cleavage of short modified DNA by restriction endonuclease BamHI‐HF. Finally, DNA template containing U E was used for in vitro transcription with E. coli RNA polymerase and the transcription was turned off by CuAAC with 3‐azidopropane‐1,2‐diol or 3‐azido‐7‐hydroxycoumarin.