title: Divergent subunit interactions among fungal mRNA 5'-capping machineries.
abstract: The Saccharomyces cerevisiae mRNA capping enzyme consists of two subunits: an RNA 5'-triphosphatase (RTPase) and GTP::mRNA guanylyltransferase (GTase). The GTase subunit (Ceg1) binds to the phosphorylated carboxyl-terminal domain of the largest subunit (CTD-P) of RNA polymerase II (pol II), coupling capping with transcription. Ceg1 bound to the CTD-P is inactive unless allosterically activated by interaction with the RTPase subunit (Cet1). For purposes of comparison, we characterize here the related GTases and RTPases from the yeasts Schizosaccharomyces pombe and Candida albicans. Surprisingly, the S. pombe capping enzyme subunits do not interact with each other. Both can independently interact with CTD-P of pol II, and the GTase is not repressed by CTD-P binding. The S. pombe RTPase gene (pct1+) is essential for viability. Pct1 can replace the S. cerevisiae RTPase when GTase activity is supplied by the S. pombe or mouse enzymes but not by the S. cerevisiae GTase. The C. albicans capping enzyme subunits do interact with each other. However, this interaction is not essential in vivo. Our results reveal an unexpected diversity among the fungal capping machineries.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 021151, USA.
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Takagi
authors.forename: Eun-Jung
authors.initials: EJ
authors.lastname: Cho
authors.forename: Rozmin T K
authors.initials: RT
authors.lastname: Janoo
authors.forename: Vladimir
authors.initials: V
authors.lastname: Polodny
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Takase
authors.forename: Michael C
authors.initials: MC
authors.lastname: Keogh
authors.forename: Sue-Ann
authors.initials: SA
authors.lastname: Woo
authors.forename: Lucille D
authors.initials: LD
authors.lastname: Fresco-Cohen
authors.forename: Charles S
authors.initials: CS
authors.lastname: Hoffman
authors.forename: Stephen
authors.initials: S
authors.lastname: Buratowski
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002176:Candida albicans / Q000201:enzymology / Q000235:genetics; D004257:DNA Polymerase II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004271:DNA, Fungal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005658:Fungi / Q000201:enzymology* / Q000235:genetics; D005800:Genes, Fungal; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D021122:Protein Subunits; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D012568:Schizosaccharomyces / Q000201:enzymology / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D000098556:mRNA Guanylyltransferases
chemical_list: D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D021122:Protein Subunits; D029702:Schizosaccharomyces pombe Proteins; C087021:res2 protein, S pombe; D009713:Nucleotidyltransferases; D000098556:mRNA Guanylyltransferases; D004257:DNA Polymerase II; D017766:Acid Anhydride Hydrolases; C023090:RNA triphosphatase