A yeast-based genetic system for functional analysis of viral mRNA capping enzymes Journal Article
| Authors: | Ho, C. K.; Martins, A.; Shuman, S. |
| Article Title: | A yeast-based genetic system for functional analysis of viral mRNA capping enzymes |
| Abstract: | Virus-encoded mRNA capping enzymes are attractive targets for antiviral therapy, but functional studies have been limited by the lack of genetically tractable in vivo systems that focus exclusively on the RNA-processing activities of the viral proteins. Here we have developed such a system by engineering a viral capping enzyme - vaccinia virus D1(1-545)p, an RNA triphosphatase and RNA guanylyltransferase - to function in the budding yeast Saccharomyces cerevisiae in lieu of the endogenous fungal triphosphatase (Cet1p) and guanylyltransferase (Ceg1p). This was accomplished by fusion of D1(1-545)p to the C-terminal guanylyltransferase domain of mammalian capping enzyme, Mce1 (211-597) p, which serves as a vehicle to target the viral capping enzyme to the RNA polymerase II elongation complex. An inactivating mutation (K294A) of the mammalian guanylyltransferase active site in the fusion protein had no impact on genetic complementation of cet1Δceg1 Δ cells, thus proving that (i) the viral guanylyltransferase was active in vivo and (ii) the mammalian domain can serve purely as a chaperone to direct other proteins to the transcription complex. Alanine scanning had identified five amino acids of vaccinia virus capping enzyme - Glu37, Glu39, Arg77, Glu192, and Glu194 - that are essential for γ phosphate cleavage in vitro. Here we show that the introduction of mutation E37A, R77A, or E192A into the fusion protein abrogates RNA triphosphatase function in vivo. The essential residues are located within three motifs that define a family of vital and fungal metal-dependent phosphohydrolases with a distinctive capacity to hydrolyze nucleoside triphosphates to nucleoside diphosphates in the presence of manganese or cobalt. The acidic residues Glu37, Glu39, and Glu192 likely comprise the metal-binding site of vaccinia virus triphosphatase, insofar as their replacement by glutamine abolishes the RNA triphosphatase and ATPase activities. |
| Keywords: | mutation; nonhuman; animals; mice; phosphatase; ph; enzyme activity; acid anhydride hydrolases; methyltransferases; amino acid sequence; recombinant fusion proteins; genetic engineering; messenger rna; virus rna; saccharomyces cerevisiae; rna, messenger; vaccinia virus; binding sites; multienzyme complexes; enzyme binding; catalytic domain; rna polymerase ii; adenosine triphosphatases; hydrolysis; phosphoric monoester hydrolases; hydrogen-ion concentration; metals; amino acid motifs; rna capping; genetic complementation test; nucleotidyltransferases; genes, fungal; transferase; genes, viral; priority journal; article |
| Journal Title: | Journal of Virology |
| Volume: | 74 |
| Issue: | 12 |
| ISSN: | 0022-538X |
| Publisher: | American Society for Microbiology |
| Date Published: | 2000-06-01 |
| Start Page: | 5486 |
| End Page: | 5494 |
| Language: | English |
| DOI: | 10.1128/jvi.74.12.5486-5494.2000 |
| PUBMED: | 10823853 |
| PROVIDER: | scopus |
| PMCID: | PMC112033 |
| DOI/URL: | |
| Notes: | Export Date: 18 November 2015 -- Source: Scopus |
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