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J. Bacteriol., 07 1997, 4419-4425, Vol 179, No. 13
MV Francia, P Avila, F de la Cruz and JM Garcia Lobo
Integron In2 integrase (IntI1)-mediated site-specific recombination between
two primary sites occurs at a high frequency, while that between a primary
and a secondary site occurs at frequencies around 10,000 times lower.
Secondary sites consist of a pentanucleotide with only two fully conserved
residues (GWTMW). The analysis of IntI1- mediated recombinants in the
plasmid pOX38 revealed the existence in this plasmid of a site used at a
frequency intermediate between those of primary and secondary sites.
Analysis of this site showed two potentially relevant structural features:
first, a set of two consensus pentanucleotides, separated by 5 bp and in
opposite orientations, forming what will be called a double site; and
second, a longer sequence with some extent of sequence symmetry with the
double site at its 3' end. A recombinant plasmid, pSU18P, containing a
double site was constructed. Examination of R388-pSU18P recombinants showed
that double sites were used preferentially over single pentanucleotides by
IntI1. Comparisons of the nucleotide sequences of known 59-bp elements
showed that in most cases there was a double site at each element end.
Mutagenesis of the F hot spot was carried out to make it look more like the
consensus 59-bp element. The improved sites showed recombination
frequencies and specificities almost comparable to those observed at IntI1
primary sites.
Copyright © 1997, American Society for Microbiology
A hot spot in plasmid F for site-specific recombination mediated by Tn21 integron integrase
Departamento de Biologia Molecular, Facultad de Medicina, Universidad de Cantabria, Santander, Spain.
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