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. Author manuscript; available in PMC: 2016 Nov 1.
Published in final edited form as: Biochim Biophys Acta. 2015 Apr 30;1854(11):1801–1808. doi: 10.1016/j.bbapap.2015.04.022

Fig. 2.

Fig. 2

Reaction pathways and transition states for RNA 2’-O-transphosphorylation in solution. Acid catalysis of the neutral diester (1) and monoanion (2) involve stepwise mechanisms via a phosphorane that may be neutral (Ineutral) or monoanionic (Imonoanion). Scheme 3 shows the potential stepwise (via a dianionic phosphorane, Idianion) and concerted (via a single transition state, TSc) mechanisms for base catalysis. Stepwise mechanisms are associative involving first a transition state for 2’O nucleophilic attack (TS1) and a second transition state for breakdown of the intermediate by departure of the 5’O leaving group.