title: Structural requirement for Mg2+ binding in the group I intron core.
abstract: Divalent metal ions are required for splicing of group I introns, but their role in maintaining the structure of the active site is still under investigation. Ribonuclease and hydroxyl radical footprinting of a small group I intron from Azoarcus pre-tRNA(Ile) showed that tertiary interactions between helical domains are stable in a variety of cations. Only Mg(2+), however, induced a conformational change in the intron core that correlates with self-splicing activity. Three metal ion binding sites in the catalytic core were identified by Tb(III)-dependent cleavage. Two of these are near bound substrates in a three-dimensional model of the ribozyme. A third metal ion site is near an A minor motif in P3. In the pre-tRNA, Tb(3+) cleavage was redirected to the 5' and 3' splice sites, consistent with metal-dependent activation of splice site phosphodiesters. The results show that many counterions induce global folding, but organization of the group I active site is specifically linked to Mg(2+) binding at a few sites.
authors.affiliation: T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218-4118, USA.
authors.forename: Prashanth
authors.initials: P
authors.lastname: Rangan
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Woodson
mesh_terms: D020627:Azoarcus / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D017124:Conserved Sequence / Q000235:genetics; D005091:Exons / Q000235:genetics; D007438:Introns / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012322:RNA Precursors; D022821:RNA Splice Sites / Q000235:genetics; D012329:RNA, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012355:RNA, Transfer, Ile / Q000737:chemistry / Q000235:genetics*; D013379:Substrate Specificity
chemical_list: D012322:RNA Precursors; D022821:RNA Splice Sites; D012329:RNA, Bacterial; D012355:RNA, Transfer, Ile; D008274:Magnesium