LAUSR

There is a need for methods to chemically incorporate photocleavable labels into synthetic and biologically sourced nucleic acids in a chemically defined and reversible manner. We have previously demonstrated that the light‐cleaved diazo di‐methoxy nitro phenyl ethyl (diazo‐DMNPE) group has a remarkable regiospecificity for modifying terminally phosphorylated siRNA. Building on this observation, we have identified conditions under which a diazo‐DMNPE reagent that we designed (diazo‐DMNPE‐azide or DDA) is able to singly modify any nucleic acid (RNA, DNA, single‐stranded, double‐stranded, 3′ or 5′ phosphate). It can then be modified with any clickable reagent to incorporate arbitrary labels such as fluorophores into the nucleic acid. Finally, native nucleic acid can be regenerated directly through photolysis of the reagent. Use of the described approach should allow for the tagging of any nucleic acid, from any source—natural or unnatural—while allowing for the light‐induced regeneration of native nucleic acid.