Publications

• Saccharomyces cerevisiae Thg1 uses 5'-pyrophosphate removal to control addition of nucleotides to tRNA(His.).

  Smith B.A., Jackman J.E.

  In eukaryotes, the tRNA(His) guanylyltransferase (Thg1) catalyzes 3'-5' addition of a single guanosine residue to the -1 position (G-1) of tRNA(His), across from a highly conserved adenosine at position 73 (A73). After addition of G-1, Thg1 removes pyrophosphate from the tRNA 5'-end, generating 5' ... >> More

  In eukaryotes, the tRNA(His) guanylyltransferase (Thg1) catalyzes 3'-5' addition of a single guanosine residue to the -1 position (G-1) of tRNA(His), across from a highly conserved adenosine at position 73 (A73). After addition of G-1, Thg1 removes pyrophosphate from the tRNA 5'-end, generating 5'-monophosphorylated G-1-containing tRNA. The presence of the 5'-monophosphorylated G-1 residue is important for recognition of tRNA(His) by its cognate histidyl-tRNA synthetase. In addition to the single-G-1 addition reaction, Thg1 polymerizes multiple G residues to the 5'-end of tRNA(His) variants. For 3'-5' polymerization, Thg1 uses the 3'-end of the tRNA(His) acceptor stem as a template. The mechanism of reverse polymerization is presumed to involve nucleophilic attack of the 3'-OH from each incoming NTP on the intact 5'-triphosphate created by the preceding nucleotide addition. The potential exists for competition between 5'-pyrophosphate removal and 3'-5' polymerase reactions that could define the outcome of Thg1-catalyzed addition, yet the interplay between these competing reactions has not been investigated for any Thg1 enzyme. Here we establish transient kinetic assays to characterize the pyrophosphate removal versus nucleotide addition activities of yeast Thg1 with a set of tRNA(His) substrates in which the identity of the N-1:N73 base pair was varied to mimic various products of the N-1 addition reaction catalyzed by Thg1. We demonstrate that retention of the 5'-triphosphate is correlated with efficient 3'-5' reverse polymerization. A kinetic partitioning mechanism that acts to prevent addition of nucleotides beyond the -1 position with wild-type tRNA(His) is proposed. << Less

  Biochemistry 53:1380-1391(2014) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• Identification of distinct biological functions for four 3'-5' RNA polymerases.

  Long Y., Abad M.G., Olson E.D., Carrillo E.Y., Jackman J.E.

  The superfamily of 3'-5' polymerases synthesize RNA in the opposite direction to all other DNA/RNA polymerases, and its members include eukaryotic tRNA(His) guanylyltransferase (Thg1), as well as Thg1-like proteins (TLPs) of unknown function that are broadly distributed, with family members in all ... >> More

  The superfamily of 3'-5' polymerases synthesize RNA in the opposite direction to all other DNA/RNA polymerases, and its members include eukaryotic tRNA(His) guanylyltransferase (Thg1), as well as Thg1-like proteins (TLPs) of unknown function that are broadly distributed, with family members in all three domains of life. Dictyostelium discoideum encodes one Thg1 and three TLPs (DdiTLP2, DdiTLP3 and DdiTLP4). Here, we demonstrate that depletion of each of the genes results in a significant growth defect, and that each protein catalyzes a unique biological reaction, taking advantage of specialized biochemical properties. DdiTLP2 catalyzes a mitochondria-specific tRNA(His) maturation reaction, which is distinct from the tRNA(His) maturation reaction typically catalyzed by Thg1 enzymes on cytosolic tRNA. DdiTLP3 catalyzes tRNA repair during mitochondrial tRNA 5'-editing in vivo and in vitro, establishing template-dependent 3'-5' polymerase activity of TLPs as a bona fide biological activity for the first time since its unexpected discovery more than a decade ago. DdiTLP4 is cytosolic and, surprisingly, catalyzes robust 3'-5' polymerase activity on non-tRNA substrates, strongly implying further roles for TLP 3'-5' polymerases in eukaryotes. << Less

  Nucleic Acids Res 44:8395-8406(2016) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• Doing it in reverse: 3'-to-5' polymerization by the Thg1 superfamily.

  Jackman J.E., Gott J.M., Gray M.W.

  The tRNA(His) guanylyltransferase (Thg1) family of enzymes comprises members from all three domains of life (Eucarya, Bacteria, Archaea). Although the initial activity associated with Thg1 enzymes was a single 3'-to-5' nucleotide addition reaction that specifies tRNA(His) identity in eukaryotes, t ... >> More

  The tRNA(His) guanylyltransferase (Thg1) family of enzymes comprises members from all three domains of life (Eucarya, Bacteria, Archaea). Although the initial activity associated with Thg1 enzymes was a single 3'-to-5' nucleotide addition reaction that specifies tRNA(His) identity in eukaryotes, the discovery of a generalized base pair-dependent 3'-to-5' polymerase reaction greatly expanded the scope of Thg1 family-catalyzed reactions to include tRNA repair and editing activities in bacteria, archaea, and organelles. While the identification of the 3'-to-5' polymerase activity associated with Thg1 enzymes is relatively recent, the roots of this discovery and its likely physiological relevance were described ≈ 30 yr ago. Here we review recent advances toward understanding diverse Thg1 family enzyme functions and mechanisms. We also discuss possible evolutionary origins of Thg1 family-catalyzed 3'-to-5' addition activities and their implications for the currently observed phylogenetic distribution of Thg1-related enzymes in biology. << Less

  RNA 18:886-899(2012) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.