title: Conserved target for group II intron insertion in relaxase genes of conjugative elements of gram-positive bacteria.
abstract: The lactococcal group II intron Ll.ltrB interrupts the ltrB relaxase gene within a region that encodes a conserved functional domain. Nucleotides essential for the homing of Ll.ltrB into an intronless version of ltrB are found exclusively at positions required to encode amino acids broadly conserved in a family of relaxase proteins of gram-positive bacteria. Two of these relaxase genes, pcfG from the enterococcal plasmid pCF10 and the ORF4 gene in the streptococcal conjugative transposon Tn5252, were shown to support Ll.ltrB insertion into the conserved motif at precisely the site predicted by sequence homology with ltrB. Insertion occurred through a mechanism indistinguishable from retrohoming. Splicing and retention of conjugative function was demonstrated for pCF10 derivatives containing intron insertions. Ll.ltrB targeting of a conserved motif of a conjugative element suggests a mechanism for group II intron dispersal among bacteria. Additional support for this mechanism comes from sequence analysis of the insertion sites of the E.c.I4 family of bacterial group II introns.
authors.affiliation: Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Jack H
authors.initials: JH
authors.lastname: Staddon
authors.forename: Edward M
authors.initials: EM
authors.lastname: Bryan
authors.forename: Dawn A
authors.initials: DA
authors.lastname: Manias
authors.forename: Gary M
authors.initials: GM
authors.lastname: Dunny
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D003227:Conjugation, Genetic; D004254:DNA Nucleotidyltransferases / Q000235:genetics*; D004251:DNA Transposable Elements / Q000235:genetics; D018390:Gene Targeting; D005798:Genes, Bacterial; D006094:Gram-Positive Bacteria / Q000235:genetics*; D007438:Introns; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C099786:LtrB protein, Lactococcus lactis; D004254:DNA Nucleotidyltransferases; C110340:DNA relaxase