Large-scale allosteric switch in the 7SK RNA regulates transcription in response to growth and stress
7SK is a highly conserved non-coding RNA that regulates eukaryotic transcription by sequestering positive transcription elongation factor b (P-TEFb). 7SK regulatory function likely entails changes in RNA structure, but characterizing dynamic RNA-protein complexes in cells has remained an unsolved challenge. We describe a new chemical probing strategy (DANCE-MaP) that uses maximum likelihood deconvolution and probabilistic read assignment to define simultaneously (i) per-nucleotide reactivity profiles, (ii) direct base pairing interactions, and (iii) tertiary and higher-order interactions for each conformation of multi-state RNA structural ensembles, all from a single experiment. We show that human 7SK RNA, despite significant heterogeneity, intrinsically codes for a large-scale structural switch that couples dissolution of the P-TEFb binding site to structural remodeling at distal release factor binding sites. The 7SK structural equilibrium is regulated by cell type, shifts dynamically in response to cell growth and stress, and can be exogenously targeted to modulate transcription in cells. Our data support that the 7SK structural ensemble functions as an integrator of diverse cellular signals to control transcription elongation in environment and cell specific ways, and establishes DANCE-MaP as a powerful strategy for comprehensively defining RNA structure and dynamics in cells.