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The S.ma.I2 class C group II intron inserts at integron attC sites

¹ Departamento de Microbiología, Inmunología y Parasitología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
² Centre de Recherche en Infectiologie, Université Laval, Québec, Canada
³ Département de Biochimie et de Microbiologie, Université Laval, Québec, Canada

Correspondence
Daniela Centrón
dcentron{at}gmail.com

We previously found the class C S.ma.I2 group II (GII) intron in Serratia marcescens SCH909 inserted into the variable region of a class 1 integron within the attC site of the ant(2'')-Ia gene cassette. Here, we demonstrate that this ant(2'')-Ia : : S.ma.I2 gene cassette is a recombinationally active element despite the presence of the S.ma.I2 intron. In addition, S.ma.I2 is an active GII intron capable of performing self-splicing and invading specific target sites. Intron homing to a DNA target site is RecA-independent and recognizes the intron binding site (IBS)1 and IBS3 regions, formed by the 5' TTGTT 3' consensus sequence located within the inverse core site of attC integrons. Our results also indicate that the process for S.ma.I2 intron mobilization involves a secondary structure provided by the folding of the complete attC site. Moreover, phylogenetic analysis of the class C GII introns showed a clear divergent clade formed by introns that insert within specific sites usually associated with lateral gene transfer.

A supplementary table showing the GII intron and E1 sequences used in this study, and two supplementary figures showing the structures used for intron self-splicing and the secondary structures of the target sites corresponding to class C GII introns, are available with the online version of this paper.