title: The mechanism of U insertion/deletion RNA editing in kinetoplastid mitochondria.
abstract: Recent advances in in vitrosystems and identification of putative enzymatic activities have led to the acceptance of a modified 'enzyme cascade' model for U insertion/deletion RNA editing in kinetoplastid mitochondria. Models involving the transfer of uridines (Us) from the 3'-end of gRNA to the editing site appear to be untenable. Two types of in vitrosystems have been reported: (i) a gRNA-independent U insertion activity that is dependent on the secondary structure of the mRNA; (ii) a gRNA-dependent U insertion activity that requires addition of a gRNA that can form an anchor duplex with the pre-edited mRNA and which contains guiding A and G nucleotides to base pair with the added Us. In the case of the gRNA-mediated reaction, the precise site of cleavage is at the end of the gRNA-mRNA anchor duplex, as predicted by the original model. The model has been modified to include the addition of multiple Us to the 3'-end of the 5'-cleavage fragment, followed by the formation of base pairs with the guiding nucleotides and trimming back of the single-stranded oligo(U) 3'-overhang. The two fragments, which are held together by the gRNA 'splint', are then ligated. Circumstantial in vitroevidence for involvement of an RNA ligase and an endoribonuclease, which are components of a 20S complex, was obtained. Efforts are underway in several laboratories to isolate and characterize specific components of the editing machinery.
authors.affiliation: Howard Hughes Medical Institute and Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA 90095-1662, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Alfonzo
authors.forename: O
authors.initials: O
authors.lastname: Thiemann
authors.forename: L
authors.initials: L
authors.lastname: Simpson
mesh_terms: D000818:Animals; D018503:Genome, Protozoan; D016830:Kinetoplastida / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D012313:RNA / Q000378:metabolism; D017393:RNA Editing; D017394:RNA, Guide, Kinetoplastida / Q000378:metabolism; D000077278:RNA, Mitochondrial; D016053:RNA, Protozoan / Q000378:metabolism; D014529:Uridine / Q000378:metabolism
chemical_list: D000077278:RNA, Mitochondrial; D016053:RNA, Protozoan; D012313:RNA; D014529:Uridine; D017394:RNA, Guide, Kinetoplastida