Survey of chimeric IStron elements in bacterial genomes: multiple molecular symbioses between group I intron ribozymes and DNA transposons.
Bottom Line: IStrons are therefore a striking example of a molecular symbiosis between unrelated genetic elements endowed with different functions.We show that IStrons have a restricted phylogenetic distribution limited to two bacterial phyla, the Firmicutes and the Fusobacteria.In addition, introns and IS elements related to those that were at the origin of IStrons were also identified.
Affiliation: Laboratory for Microbial Dynamics (LaMDa), Department of Pharmaceutical Biosciences, University of Oslo, Oslo, Norway Institut de Biologie Physico-Chimique, UMR CNRS 7141, Université Pierre et Marie Curie, Paris, France email@example.com.Show MeSH
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Mentions: Multiple sequence alignment showing the IStron target sites, boundaries and sequence ends. Omitted regions are indicated by the sign ‘[…]’. GenBank accession numbers of genomic sequences encoding the IStrons shown are given in parentheses next to IStron names. IStron-less sequences homologous to IStron flanking exons are included to confirm IStron boundaries (sequences named by their GenBank accession numbers only). Also included are IS elements (ISDra2 and ISBth15 from D. radiodurans and B. thuringiensis, respectively, taken from the ISfinder database) and group I introns (GenBank accessions ACJY01000107 and ADMN01000043 from F. periodonticum and T. sanguinis, respectively) with ends and target sites similar to those of IStrons. Group A and B IStrons are inserted next to T-rich pentanucleotide and GG-containing sites, respectively, which are boxed in cyan. Note that the target site of group B IStrons does not end with a U, unlike for virtually all known group I introns. In group A IStrons, the regions corresponding to the subterminal palindromes that are recognized by the ORF A transposase during transposition of IS200/IS605 elements are highlighted in yellow. For group B IStrons, imperfect AT-rich IR motifs that are presumed to be recognized by the ORF A transposase during transposition of IS607 elements are highlighted in light blue. IR motifs forming the IR stem in the group I intron structure of IStrons (see Figure 4) are boxed in black. The direct repeat sequence (3′ DR) that is similar to part of the 5′ IR motif (5′ IR/5′ DR) and that is located immediately upstream of, and is globally complementary to, the 3′ IR motif in group B IStrons is boxed in yellow.
Affiliation: Laboratory for Microbial Dynamics (LaMDa), Department of Pharmaceutical Biosciences, University of Oslo, Oslo, Norway Institut de Biologie Physico-Chimique, UMR CNRS 7141, Université Pierre et Marie Curie, Paris, France firstname.lastname@example.org.