TYW1 catalyzes the condensation of N-methylguanosine with two carbon atoms from an unknown second substrate to form 4-demethylwyosine, which is a common intermediate in the biosynthesis of all of the hypermodified RNA bases related to wybutosine found in eukaryal and archaeal tRNA Phe. Of the potential substrates examined, only incubation with pyruvate resulted in formation of 4-demethylwyosine. Moreover, incubation with C1, C2, C3, or C1,2,3- 13C-labeled pyruvate showed that C2 and C3 are incorporated while C1 is not. The mechanistic implications of these results are discussed in the context of the structure of TYW1.
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