title: The 2'-O-ribose methyltransferase for cap 1 of spliced leader RNA and U1 small nuclear RNA in Trypanosoma brucei.
abstract: mRNA cap 1 2'-O-ribose methylation is a widespread modification that is implicated in processing, trafficking, and translational control in eukaryotic systems. The eukaryotic enzyme has yet to be identified. In kinetoplastid flagellates trans-splicing of spliced leader (SL) to polycistronic precursors conveys a hypermethylated cap 4, including a cap 0 m7G and seven additional methylations on the first 4 nucleotides, to all nuclear mRNAs. We report the first eukaryotic cap 1 2'-O-ribose methyltransferase, TbMTr1, a member of a conserved family of viral and eukaryotic enzymes. Recombinant TbMTr1 methylates the ribose of the first nucleotide of an m7G-capped substrate. Knockdowns and null mutants of TbMTr1 in Trypanosoma brucei grow normally, with loss of 2'-O-ribose methylation at cap 1 on substrate SL RNA and U1 small nuclear RNA. TbMTr1-null cells have an accumulation of cap 0 substrate without further methylation, while spliced mRNA is modified efficiently at position 4 in the absence of 2'-O-ribose methylation at position 1; downstream cap 4 methylations are independent of cap 1. Based on TbMTr1-green fluorescent protein localization, 2'-O-ribose methylation at position 1 occurs in the nucleus. Accumulation of 3'-extended SL RNA substrate indicates a delay in processing and suggests a synergistic role for cap 1 in maturation.
authors.affiliation: Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine, 609 Charles E. Young Drive East, University of California at Los Angeles, Los Angeles, CA 90095-1489, USA.
authors.forename: Jesse R
authors.initials: JR
authors.lastname: Zamudio
authors.forename: Bidyottam
authors.initials: B
authors.lastname: Mittra
authors.forename: Silvie
authors.initials: S
authors.lastname: Foldynová-Trantírková
authors.forename: Gusti M
authors.initials: GM
authors.lastname: Zeiner
authors.forename: Julius
authors.initials: J
authors.lastname: Lukes
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Sturm
authors.forename: David A
authors.initials: DA
authors.lastname: Campbell
mesh_terms: D000818:Animals; D008745:Methylation; D008780:Methyltransferases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D010641:Phenotype; D010802:Phylogeny; D015800:Protozoan Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D012315:RNA Caps; D034622:RNA Interference; D016053:RNA, Protozoan; D012342:RNA, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D020038:RNA, Spliced Leader / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020040:Trans-Splicing; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism
chemical_list: D015800:Protozoan Proteins; D012315:RNA Caps; D016053:RNA, Protozoan; D012342:RNA, Small Nuclear; D020038:RNA, Spliced Leader; D011993:Recombinant Fusion Proteins; C405483:U1 small nuclear RNA; D008780:Methyltransferases