Application： 1-Methyl-7-nitroisatoic anhydride (1M7) is used as an in vivo SHAPE-MaP reagent for live cell RNA structure analysis at single nucleotide resolution. SHAPE -- or selective 2′-hydroxyl acylation analyzed by primer extension -- uses small, electrophilic chemical probes such as 1M7 to react with the 2′-hydroxyl group and provides insight to RNA structure. When combined with mutational profiling (MaP), quantitative nucleotide measurements are possible for entire transciptomes. Together, these methods deepen the understanding of RNA interactions and regions that may be exploited for design of RNA-targeting small-molecule drugs.