Talk title Bridging the gap between RNA editing and modification: A 10‐year solution to a 25‐year problem

Abstract

All types of nucleic acids in cells undergo naturally occurring chemical modifications, including DNA, rRNA, mRNA, snRNA, and most prominently tRNA. Over 100 different modifications have been described and every position in the purine and pyrimidine bases has been seen modified; the sugar is often also modified. Despite recent progress, the mechanism for the synthesis of most modifications is not fully understood partly due to difficulty in reconstituting modification enzyme activity in vitro. Cytosine to uridine (C to U) editing of tRNAs in eukaryotes was first discovered over 20 years ago, yet due to the lack of an in vitro assay, the editing enzyme is still at large and the editing mechanism remains unsolved. In this work we show that cytosine 32 in the anticodon loop of tRNAThr is methylated to 3‐methylcytosine (m3C) as a pre‐requisite for C to U deamination. Formation of m3C in vitro requires the presence of both TbTRM140 (the m3C methyltransferase) and the TbADAT2/3 (the A to I editing deaminase). Once m3C is formed the same set of enzymes are required for further deamination from m3C to form 3‐methyluridine (m3U). In our previous work, we also showed that TbADAT2/3 was a highly mutagenic enzyme randomly deaminating DNA. Now we provide evidence that when co‐expressed with the methylase its mutagenic ability is kept in check via complex formation with TRM140. This helps explain how T. brucei escapes “wholesale deamination” of its genome while harboring both enzymes in its nuclear compartment. This observation has implications for the control of another mutagenic deaminase, human AID, and provides a rationale for its regulation.Support or Funding InformationNIH GM084065This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.