Poster abstracts

Poster number 9 submitted by Frank Ragone

A Single Enzyme is Required for Both C to U and A to I Deamination Editing

Frank Ragone (Microbiology / The Ohio State University), Mary Anne T. Rubio (Microbiology / The Ohio State University), Kirk W. Gaston (Microbiology / The Ohio State University), Juan D. Alfonzo (Microbiology / The Ohio State University)

Abstract:
Editing of tRNAs is widespread in nature and either changes the decoding properties or restores the folding of a tRNA. Unlike the phylogenetically disperse adenosine (A) to inosine (I) editing (occurring in all domains of life), cytosine (C) to uridine (U) editing has only been previously described in organellar tRNAs. We have shown that cytoplasmic tRNAThr(AGU) undergoes two distinct editing events in the anticodon loop: C to U and A to I. In vivo, every inosine containing tRNAThr(AGU) is also edited at position 32. In vitro, C to U editing stimulates the essential conversion of A to I at the wobble base. Surprisingly, enzymes mediating tRNA deamination in bacteria and yeast contain conserved cytidine deaminase motifs, suggesting an evolutionary link between the two reactions. In trypanosomatids, the enzyme responsible for either reaction has not been identified. Here, we show that one trypanosomatid enzyme TbADAT2p can mediate A to I editing in vitro and is required for both editing reactions in vivo. Thus, a single deaminase can mediate two tRNA editing events, providing a model for a multi-specificity editing enzyme. We suggest that the observed flexibility of the TbADAT2 protein is an inherent characteristic of the ancestor deaminase domain. Substrate specificity of this enzyme family might have then evolved by appending this flexible catalytic module onto different protein scaffolds.

Keywords: tRNA, Editing, Deamination