tRNAHis maturation: an essential yeast protein catalyzes addition of a guanine nucleotide to the 5' end of tRNAHis

Genes Dev. 2003 Dec 1;17(23):2889-901. doi: 10.1101/gad.1148603. Epub 2003 Nov 21.


All tRNAHis molecules are unusual in having an extra 5' GMP residue (G(-1)) that, in eukaryotes, is added after transcription and RNase P cleavage. Incorporation of this G(-1) residue is a rare example of nucleotide addition occurring at an RNA 5' end in a normal phosphodiester linkage. We show here that the essential Saccharomyces cerevisiae ORF YGR024c (THG1) is responsible for this guanylyltransferase reaction. Thg1p was identified by survey of a genomic collection of yeast GST-ORF fusion proteins for addition of [alpha-32P]GTP to tRNAHis. End analysis confirms the presence of G(-1). Thg1p is required for tRNAHis guanylylation in vivo, because cells depleted of Thg1p lack G(-1) in their tRNAHis. His6-Thg1p purified from Escherichia coli catalyzes the guanylyltransferase step of G(-1) addition using a ppp-tRNAHis substrate, and appears to catalyze the activation step using p-tRNAHis and ATP. Thg1p is highlye conserved in eukaryotes, where G(-1) addition is necessary, and is not found in eubacteria, where G(-1) is genome-encoded. Thus, Thg1p is the first member of a new family of enzymes that can catalyze phosphodiester bond formation at the 5' end of RNAs, formally in a 3'-5' direction. Surprisingly, despite its varied activities, Thg1p contains no recognizable catalytic or functional domains.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Catalysis
  • DNA Primers
  • Guanine Nucleotides / metabolism*
  • Molecular Sequence Data
  • Nucleotidyltransferases / chemistry
  • Nucleotidyltransferases / genetics
  • Nucleotidyltransferases / metabolism
  • Open Reading Frames
  • RNA Processing, Post-Transcriptional*
  • RNA, Transfer, His / metabolism*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Homology, Amino Acid


  • DNA Primers
  • Guanine Nucleotides
  • RNA, Transfer, His
  • Saccharomyces cerevisiae Proteins
  • Nucleotidyltransferases
  • guanylyltransferase