title: Trypanosoma brucei mitochondrial guide RNA-mRNA chimera-forming activity cofractionates with an editing-domain-specific endonuclease and RNA ligase and is mimicked by heterologous nuclease and RNA ligase.
abstract: RNA editing in trypanosomes has been proposed to occur through transesterification or endonuclease cleavage and RNA ligation reactions. Both models involve a chimeric intermediate in which a guide RNA (gRNA) is joined through its 3' oligo(U) tail to an editing site of the corresponding mRNA. Velocity centrifugation of Trypanosoma brucei mitochondrial extracts had been reported to completely separate the gRNA-mRNA chimera-forming activity from endonuclease activity (V. W. Pollard, M. E. Harris, and S. L. Hajduk, EMBO J. 11:4429-4438, 1992), appearing to rule out the endonuclease-RNA ligase mechanism. However, we show that an editing-domain-specific endonuclease activity does cosediment with the chimera-forming activity, as does the RNA ligase activity, but detection of the specific endonuclease requires reducing assay conditions. This report further demonstrates that the T. brucei chimera-forming activity is mimicked by mung bean nuclease and T4 RNA ligase. Using cytochrome b (CYb) preedited mRNA and a model CYb gRNA, we found that these heterologous enzymes specifically generate CYb gRNA-mRNA chimeras analogous to those formed in the mitochondrial extract. These combined results provide support for the endonuclease-RNA ligase mechanism of chimera formation.
authors.affiliation: Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Piller
authors.forename: C J
authors.initials: CJ
authors.lastname: Decker
authors.forename: L N
authors.initials: LN
authors.lastname: Rusché
authors.forename: B
authors.initials: B
authors.lastname: Sollner-Webb
mesh_terms: D000818:Animals; D001483:Base Sequence; D004720:Endonucleases / Q000378:metabolism; D008969:Molecular Sequence Data; D012313:RNA / Q000378:metabolism; D017393:RNA Editing; D011130:RNA Ligase (ATP) / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D000077278:RNA, Mitochondrial; D016053:RNA, Protozoan / Q000378:metabolism*; D013379:Substrate Specificity; D014346:Trypanosoma brucei brucei / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D000077278:RNA, Mitochondrial; D016053:RNA, Protozoan; D012313:RNA; D004720:Endonucleases; D011130:RNA Ligase (ATP)