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. Author manuscript; available in PMC: 2011 Jan 21.
Published in final edited form as: FEBS Lett. 2010 Jan 21;584(2):278–286. doi: 10.1016/j.febslet.2009.11.075

Figure 3.

Figure 3

Proposed mechanism for methylation at exocyclic adenine N6 by the DNA methylase M.TaqI – a potential model for tRNA methylases operating at adenine N6, guanine N2, and cytosine N4. Attack on the SAM methyl group is depicted as proceeding via attack by nitrogen in its sp2 hybridization state, because proton removal prior to nucleophilic attack is highly unfavorable. Proton abstraction from the positively charged quaternary nitrogen, by contrast, is relatively facile. See text for details.