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Cover Picture: Solution Structure of Domain 6 from a Self-Splicing Group II Intron Ribozyme: A Mg2+ Binding Site is Located Close to the Stacked Branch Adenosine (ChemBioChem 3/2007)
The cover picture shows the NMR solution structure of domain 6 from a group II intron ribozyme derived from the intron ai5γ located in the mitochondrial cytochrome c oxidase I gene of Saccharomyces cerevisiae. As indicated at the top, these large molecular catalytic RNAs cut themselves out of the primary RNA transcript by a two-step mechanism similar to the spliceosome. The 2'-OH of a highly conserved adenosine within domain 6 serves as the nucleophile in the first step of splicing. Our solution structure shows for the first time that this branch adenosine resides within the helix, sandwiched between two adjacent GU wobble pairs. These GU pairs thereby form an excellent binding site for a Mg2+ in the major groove. Being an essential cofactor for group II intron catalysis, this novel Mg2+ is in close enough proximity to the catalytic 2'-OH to exert its influence on catalysis. Further details on the structure and four additional Mg2+ binding sites within domain 6 can be found in the article by R. K. O. Sigel et al. on p. 306 ff.