title: An mRNA is capped by a 2', 5' lariat catalyzed by a group I-like ribozyme.
abstract: Twin-ribozyme introns are formed by two ribozymes belonging to the group I family and occur in some ribosomal RNA transcripts. The group I-like ribozyme, GIR1, liberates the 5' end of a homing endonuclease messenger RNA in the slime mold Didymium iridis. We demonstrate that this cleavage occurs by a transesterification reaction with the joining of the first and the third nucleotide of the messenger by a 2',5'-phosphodiester linkage. Thus, a group I-like ribozyme catalyzes an RNA branching reaction similar to the first step of splicing in group II introns and spliceosomal introns. The resulting short lariat, by forming a protective 5' cap, might have been useful in a primitive RNA world.
authors.affiliation: Department of Medical Biochemistry and Genetics, Panum Institute, University of Copenhagen, DK-2200N Copenhagen, Denmark. hamra@imbg.ku.dk
authors.forename: Henrik
authors.initials: H
authors.lastname: Nielsen
authors.forename: Eric
authors.initials: E
authors.lastname: Westhof
authors.forename: Steinar
authors.initials: S
authors.lastname: Johansen
mesh_terms: D001483:Base Sequence; D002384:Catalysis; D004720:Endonucleases / Q000096:biosynthesis / Q000235:genetics*; D004951:Esterification; D007438:Introns; D008969:Molecular Sequence Data; D012315:RNA Caps / Q000737:chemistry*; D012326:RNA Splicing; D016337:RNA, Catalytic / Q000737:chemistry / Q000378:metabolism*
chemical_list: C116167:GIR1 ribozyme; D012315:RNA Caps; D016337:RNA, Catalytic; D004720:Endonucleases