FINGERPRINTING THE FOLDING OF A GROUP-I PRECURSOR RNA

Evidence that folding of the Tetrahymena pre-rRNA follows a defined pa th and is rate-determining for splicing at physiological temperatures is presented. Structural isomers were separated by native polyacrylami de gel electrophoresis and their splicing activities were compared. GT P binding selectively shifts the active form of the pre RNA to an elec trophoretic band containing both spliced and unspliced RNA. In situ ch emical modification provides evidence for base-pair rearrangements in the 5' exon and structural. alterations in the intron core of partiall y and fully active forms. Transition to the fully active precursor req uires high temperature, but the activation energy is lower than expect ed for opening of RNA helices. Implications for control of RNA conform ation during splicing are discussed.