Cap methyltransferase selective binding and methylation of GpppG-RNA are stimulated by importin-alpha

Genes Dev. 2000 Dec 1;14(23):2944-9. doi: 10.1101/gad.848200.


We screened a human cDNA library for proteins that bind mRNA cap methyltransferase (MT) and isolated nuclear transporter importin-alpha (Impalpha). This direct association was confirmed by glutathione S-transferase (GST) pulldown, coimmunoprecipitation, and nuclear colocalization. In gel shift assays, MT selectively bound RNA containing 5'-terminal GpppG, and binding was inhibited by GpppG and not by m(7)GpppC. Impalpha markedly enhanced MT binding to GpppG-RNA and stimulated MT activity. MT/RNA/Impalpha complexes were dissociated by importin-beta, which also blocked the stimulation of cap methylation by Impalpha. The presence of RanGTP but not RanGDP prevented these effects of importin-beta. These findings indicate that importins play a novel role in mRNA biogenesis at the level of cap methylation.

MeSH terms

  • Cell Nucleus / metabolism
  • Dinucleoside Phosphates / metabolism*
  • Guanosine Diphosphate / metabolism
  • Guanosine Triphosphate / metabolism
  • HeLa Cells
  • Humans
  • Karyopherins
  • Methylation
  • Methyltransferases / genetics
  • Methyltransferases / metabolism*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • RNA Caps / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Structure-Activity Relationship
  • ran GTP-Binding Protein / genetics
  • ran GTP-Binding Protein / metabolism


  • Dinucleoside Phosphates
  • Karyopherins
  • Nuclear Proteins
  • RNA Caps
  • Recombinant Fusion Proteins
  • Guanosine Diphosphate
  • 7-methyl-diguanosine triphosphate
  • Guanosine Triphosphate
  • Methyltransferases
  • mRNA (guanine(N7))-methyltransferase
  • ran GTP-Binding Protein