Structure and mechanism of the RNA triphosphatase component of mammalian mRNA capping enzyme

Anita Changela, C. Kiong Ho, Alexandra Martins, Stewart Shuman, Alfonso Mondragón*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


The 5′ capping of mammalian pre-mRNAs is initiated by RNA triphosphatase, a member of the cysteine phosphatase superfamily. Here we report the 1.65 Å crystal structure of mouse RNA triphosphatase, which reveals a deep, positively charged active site pocket that can fit a 5′ triphosphate end. Structural, biochemical and mutational results show that despite sharing an HCxxxxxR(S/T) motif, a phosphoenzyme intermediate and a core α/β-fold with other cysteine phosphatases, the mechanism of phosphoanhydride cleavage by mammalian capping enzyme differs from that used by protein phosphatases to hydrolyze phosphomonoesters. The most significant difference is the absence of a carboxylate general acid catalyst in RNA triphosphatase. Residues conserved uniquely among the RNA phosphatase subfamily are important for function in cap formation and are likely to play a role in substrate recognition.

Original languageEnglish (US)
Pages (from-to)2575-2586
Number of pages12
JournalEMBO Journal
Issue number10
StatePublished - May 15 2001


  • Crystal structure
  • Cysteine phosphatase
  • MRNA capping
  • RNA processing
  • RNA triphosphatase

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)


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