Site-specific insertion of genes into integrons: role of the 59-base element and determination of the recombination cross-over point.
From examination of published DNA sequences of genes found inserted at a specific site in integrons, all genes are shown to be associated, at their 3' ends, with a short imperfect inverted repeat sequence, a 59-base element or relative of this element. The similarity of the arrangement of gene inserts in the integron and in the Tn7 transposon family is described. A refined consensus for the 59-base element is reported. Members of this family are highly diverged and the relationship of a group of longer elements to the 59-base elements is demonstrated. The ability of 59-base elements of different length and sequence to act as sites for recombination catalysed by the integron-encoded DNA integrase is demonstrated, confirming that elements of this family have a common function. The ability of elements located between gene pairs to act as recombination sites has also been demonstrated. The recombination cross-over point has been localized to the GTT triplet which is conserved in the core sites, GTTRRRY, found at the 3' end of 59-base elements. Recombination at the core site found in inverse orientation at the 5' end of the 59-base elements was not detected, and the sequences responsible for orientation of the recombination event appear to reside within the 59-base element. A model for site-specific insertion of genes into integrons and Tn7-like transposons is proposed. Circular units consisting of a gene associated with a 59-base element are inserted into an ancestral element which contains neither a gene nor a 59-base element.(ABSTRACT TRUNCATED AT 250 WORDS)
Hall
R M
RM
CSIRO Division of Biomolecular Engineering, Laboratory for Molecular Biology, North Ryde, New South Wales, Australia.
Brookes
D E
DE
Stokes
H W
HW
D001483:Base Sequence; D016384:Consensus Sequence / Q000235:genetics*; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D004251:DNA Transposable Elements / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D019426:Integrases; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional / Q000235:genetics; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*
D004251:DNA Transposable Elements; D004254:DNA Nucleotidyltransferases; D019426:Integrases