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Daniela Kruschel, Institute of Inorganic Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland and MedILS, Split
Thursday, 05.02.2009., 4 pm, MedILS lecture hall
Group II introns, which are ribozymes originating from organellar genes of plants, fungi, lower eukaryotes and many bacteria, have the ability to self-splice out of the primary RNA transcript. In addition, they can reinsert themselves into RNA and DNA, and are therefore mobile genetic elements. Metal ions are thereby strictly required for folding and catalysis. These introns consist of a conserved set of six domains (D1-D6) which are defined by characteristic secondary structural elements. D1 is not only the largest of the six domains but in addition recognizes the intron through base-pairing of two regions in D1, the exon binding sites 1 and 2 (EBS1 and EBS2) with the two intron binding sites (IBS1 and IBS2) located at the end of the 5’-exon. In this study, we used NMR spectroscopy to investigate the structural and metal ion requirements on the formation of the 5’-splice site of the group II intron ai5γ located in the cox1 gene of Saccharomyces cerevisiae. The solution structure of the system comprising the hairpin with EBS1 located in the loop was solved in the absence and presence of IBS1. Bound to IBS1, EBS1 adopts a novel conformation, which is specifically stabilized by divalent metal ions. Our results provide an important basis for an understanding of the structure and function of the splice site at atomic resolution.