RRM
2007Rustbelt RNA Meeting
RRM
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Talk abstracts
Abstract:
The tRNAHis guanylyltransferase (Thg1) catalyzes the addition of a single essential G-1 residue to the 5' end of tRNAHis, a modification that is universally conserved, is unique to histidyl-tRNA species, and is required for aminoacylation of tRNAHis in S. cerevisiae. Remarkably, Thg1 also catalyzes the template-dependent addition of multiple nucleotides in the 3'-5' direction to altered tRNA substrates; several features of this 3'-5' polymerization activity serve to distinguish it from the previously known physiological activity of Thg1, G-1 addition (Jackman & Phizicky, 2006). Since the reaction catalyzed by Thg1 is inherently unique, resulting in polymerization of nucleotides in the opposite direction of all other known DNA and RNA polymerases, and since the biological role of this unusual 3'-5' polymerization reaction remains a mystery, we have undertaken an investigation of the catalytic mechanism of nucleotide addition by Thg1, and of the substrate recognition requirements for both Thg1 activities, with the goal of defining optimal substrates for 3'-5' polymerization that could aid in the identification of in vivo substrates for this activity. Currently, we are investigating a collection of Thg1 variant proteins with alterations at highly conserved amino acids to define residues that play critical roles in G-1 addition, 3'-5' polymerization, or both activities. We are also examining the ability of Thg1 to catalyze 3'-5' polymerization with small DNA substrates, so as to consider the possibility of a previously unknown role for Thg1 in the repair or metabolism of DNA, in addition to its well-defined role in tRNA maturation.
References:
Jackman JE, Phizicky EM. 2006. tRNAHis guanylyltransferase catalyzes a 3'-5' polymerization reaction that is distinct from G-1 addition. Proc Natl Acad Sci U S A 103:8640-8645.
Keywords: Thg1, tRNAHis, 3-5 polymerase
