Probing RNA structure within living cells.

RNA folding is the most fundamental process underlying RNA function. RNA structure and associated folding paradigms have been intensively studied in vitro. However, in vivo RNA structure formation has only been explored to a limited extent. To determine the influence of the cellular environment, which differs significantly from the in vitro refolding conditions, on RNA architecture, we have applied a chemical probing technique to assess the structure of catalytic RNAs in living cells. This method is based on the fact that chemicals like dimethyl sulfate readily penetrate cells and modify specific atoms of RNA bases (N1-A, N3-C), provided that these positions are solvent accessible. By mapping the modified residues, one gains substantial information on the architecture of the target RNA on the secondary and tertiary structure level. This method also allows exploration of interactions of the target RNA with ligands such as proteins, metabolites, or other RNA molecules and associated conformational changes. In brief, in vivo chemical probing is a powerful tool to investigate RNA structure in its natural environment and can be easily adapted to study RNAs in different cell types.