Group II intron splicing in vivo by first-step hydrolysis.
Group I, group II and spliceosomal introns splice by two sequential transesterification reactions. For both spliceosomal and group II introns, the first-step reaction occurs by nucleophilic attack on the 5' splice junction by the 2' hydroxyl of an internal adenosine, forming a 2'-5' phosphodiester branch in the intron. The second reaction joins the two exons with a 3'-5' phosphodiester bond and releases intron lariat. In vitro, group II introns can self-splice by an efficient alternative pathway in which the first-step reaction occurs by hydrolysis. The resulting linear splicing intermediate participates in normal second-step reactions, forming spliced exon and linear intron RNAs. Here we show that the group II intron first-step hydrolysis reaction occurs in vivo in place of transesterification in the mitochondria of yeast strains containing branch-site mutations. As expected, the mutations block branching, but surprisingly still allow accurate splicing. This hydrolysis pathway may have been a step in the evolution of splicing mechanisms.
Podar
M
M
Department of Molecular Biology and Oncology, University of Texas Southwestern Medical Center, Dallas 75235-9148, USA.
Chu
V T
VT
Pyle
A M
AM
Perlman
P S
PS
D004951:Esterification; D005800:Genes, Fungal; D006868:Hydrolysis; D007438:Introns; D008928:Mitochondria / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D012326:RNA Splicing; D012331:RNA, Fungal / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
D012331:RNA, Fungal