RRM
2012 Rustbelt RNA Meeting
RRM
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Poster abstracts
Abstract:
The tRNAHis guanylyltransferase (Thg1) superfamily was first discovered in yeast to catalyze the post-transcriptional addition of an essential tRNAHis identity element required for HisRS recognition, a single G-1 nucleotide found at the 5’ end of almost all tRNAHis species. In most Eukarya, including yeast, this reaction forms a non-templated G-1 -A73 base pair. Previously, an alternative activity of yeast Thg1 (yThg1) was demonstrated with A73C or A73G tRNAHis substrates, where the 3’ N73CCA end was used as a template for a 3’-5’ polymerization reaction. It was predicted that this reverse polymerization was remnant of an ancestral activity, and here we show a similar occurrence in DdiTLP4, a homologue of yThg1 found in the slime mold Dictyostelium discoideum. Unlike yThg1, DdiTLP4 is predicted to participate in cytoplasmic repair of tRNA 5’ ends and has robust in vitro tRNA repair capabilities. Under limited ATP concentrations, however, DdiTLP4 catalyzes templated polymerization much like the activity described for yThg1. More importantly, we observe excessive polymerization reactions on 5’ truncated tRNA’s, the predicted substrate for DdiTLP4, as well as full length tRNAs. This suggests that the polymerization reaction may occur in vivo, yet the resulting tRNAs would contrast with the current understanding of tRNA secondary structure and function. However, we identify a mechanism where ATP is used both as a substrate and an effector molecule to control DdiTLP4 activity and inhibiting excessive nucleotide addition to full-length tRNA substrates. These result point to a novel mechanism developed by DdiTLP4 to sequester an unwanted and possibly ancestral activity.
References:
Jackman JE, Phizicky EM 2006b. tRNAHis guanylyltransferase catalyzes a 3′–5′ polymerization reaction that is distinct from G−1 addition. Proc Natl Acad Sci 103: 8640–8645.
Keywords: tRNA Biology, Thg1
