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Investigation of the Specificity of Modification Enzymes

Recognition of the anticodon by Thg1.

Recognition of the anticodon by Thg1.

Another major problem of interest to us is the nature of the substrate specificity of modification enzymes. Modification enzymes are highly specific for certain tRNA species and for specific residues within these tRNAs. This specificity can be crucial because failure of modification can lead to non-functional tRNA, and because inadvertent modification of the incorrect species can have deleterious effects on the cell. We are currently investigating the specificity of several enzymes in vivo and in vitro.

We previously examined the specificity of Thg1 for G-1 addition to tRNAHis, because G-1is crucial for histidylation of tRNAHis. Surprisingly, we found that G-1 addition is directed by the anticodon, as is true for many tRNA synthetases, but not for any other enzyme. Thus, in this case, charging specificity is achieved by a circuit in which the anticodon directs G-1 addition, which in turn directs charging of the tRNAHis with histidine.

We are currently focusing on defining the determinants of substrate specificity of other modification enzymes, with emphasis on specificity for modification of C32.

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