title: In vitro characterization of the splicing efficiency and fidelity of the RmInt1 group II intron as a means of controlling the dispersion of its host mobile element.
abstract: Group II introns are catalytic RNAs that are excised from their precursors in a protein-dependent manner in vivo. Certain group II introns can also react in a protein-independent manner under nonphysiological conditions in vitro. The efficiency and fidelity of the splicing reaction is crucial, to guarantee the correct formation and expression of the protein-coding mRNA. RmInt1 is an efficient mobile intron found within the ISRm2011-2 insertion sequence in the symbiotic bacterium Sinorhizobium meliloti. The RmInt1 intron self-splices in vitro, but this reaction generates side products due to a predicted cryptic IBS1* sequence within the 3' exon. We engineered an RmInt1 intron lacking the cryptic IBS1* sequence, which improved the fidelity of the splicing reaction. However, atypical circular forms of similar electrophoretic mobility to the lariat intron were nevertheless observed. We analyzed a run of four cytidine residues at the 3' splice site potentially responsible for a lack of fidelity at this site leading to the formation of circular intron forms. We showed that mutations of residues base-pairing in the tertiary EBS3-IBS3 interaction increased the efficiency and fidelity of the splicing reaction. Our results indicate that RmInt1 has developed strategies for decreasing its splicing efficiency and fidelity. RmInt1 makes use of unproductive splicing reactions to limit the transposition of the insertion sequence into which it inserts itself in its natural context, thereby preventing potentially harmful dispersion of ISRm2011-2 throughout the genome of its host.
authors.affiliation: Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA.
authors.forename: Isabel
authors.initials: I
authors.lastname: Chillón
authors.affiliation: Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain.
authors.forename: María Dolores
authors.initials: MD
authors.lastname: Molina-Sánchez
authors.affiliation: Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Olga
authors.initials: O
authors.lastname: Fedorova
authors.affiliation: Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain.
authors.forename: Fernando Manuel
authors.initials: FM
authors.lastname: García-Rodríguez
authors.affiliation: Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Martínez-Abarca
authors.affiliation: Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain nicolas.toro@eez.csic.es.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Toro
mesh_terms: D004251:DNA Transposable Elements / Q000235:genetics; D005091:Exons / Q000235:genetics; D007438:Introns / Q000235:genetics*; D009154:Mutation; D009690:Nucleic Acid Conformation; D012322:RNA Precursors / Q000737:chemistry / Q000235:genetics*; D012326:RNA Splicing / Q000235:genetics*; D016337:RNA, Catalytic / Q000235:genetics*; D016962:Sinorhizobium meliloti / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D012322:RNA Precursors; D016337:RNA, Catalytic
keywords: RNA circles; RmInt1; group II intron; ribozyme; splicing