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Proc Natl Acad Sci U S A. 2010 Nov 23;107(47):20305-10. doi: 10.1073/pnas.1010436107. Epub 2010 Nov 8.

tRNA(His) guanylyltransferase (THG1), a unique 3'-5' nucleotidyl transferase, shares unexpected structural homology with canonical 5'-3' DNA polymerases.

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  • 1Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405, USA.

Abstract

All known DNA and RNA polymerases catalyze the formation of phosphodiester bonds in a 5' to 3' direction, suggesting this property is a fundamental feature of maintaining and dispersing genetic information. The tRNA(His) guanylyltransferase (Thg1) is a member of a unique enzyme family whose members catalyze an unprecedented reaction in biology: 3'-5' addition of nucleotides to nucleic acid substrates. The 2.3-Å crystal structure of human THG1 (hTHG1) reported here shows that, despite the lack of sequence similarity, hTHG1 shares unexpected structural homology with canonical 5'-3' DNA polymerases and adenylyl/guanylyl cyclases, two enzyme families known to use a two-metal-ion mechanism for catalysis. The ability of the same structural architecture to catalyze both 5'-3' and 3'-5' reactions raises important questions concerning selection of the 5'-3' mechanism during the evolution of nucleotide polymerases.

Comment in

  • Crystal structure of a reverse polymerase. [Proc Natl Acad Sci U S A. 2010]
PMID:
21059936
[PubMed - indexed for MEDLINE]
PMCID:
PMC2996709
Free PMC Article

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