Unsuspected prophage-like elements in Salmonella typhimurium.
We present evidence for the existence of two large (approximately 50 kb) excisable segments in the chromosome of Salmonella typhimurium. The two elements--designated Gifsy-1 and Gifsy-2--cover, respectively, the 57 units and the 24 units of the genetic map where they contribute indicative rare restriction sites. The two elements are closely interrelated and both contain a region of sequence similarity to the recE locus of the Rac prophage of Escherichia coli. Mutations within this region of Gifsy-1 yield the classical 'Sbc' phenotype: they suppress the recombination defect of recB mutants, apparently by activating a normally silent recE-like gene. At the same time, these 'sbcE' mutations activate a Xis-type function that promotes excision of one or other of the two elements. Predictably, curing of Gifsy-1 results in the loss of recB mutant suppression. Surprisingly, the suppressor phenotype is also lost in cells cured for Gifsy-2 even though the Gifsy-1-associated sbcE mutation is still present. Moreover, the excision frequency of Gifsy-1 drops dramatically in Gifsy-2-cured cells. Thus, both elements must co-operate in the activation of recombination and excision functions. Overall, the data presented here suggest that Gifsy-1 and Gifsy-2 are cryptic prophages. They are distinct from previously described Fels prophages. Unlike Fels, they are not specific to S. typhimurium strain LT2 since they are both also found in a virulent S. typhimurium isolate (ATCC 14028s).
Figueroa-Bossi
N
N
Centre de Génétique Moleculaire, CNRS, Gif-sur-Yvette, France. Figueroa@cgm.cnrs-gif.fr
Coissac
E
E
Netter
P
P
Bossi
L
L
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D002876:Chromosomes, Bacterial / Q000378:metabolism; D004269:DNA, Bacterial / Q000032:analysis; D029968:Escherichia coli Proteins; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics*; D016153:Genes, Suppressor; D008242:Lysogeny; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012483:Salmonella Phages / Q000737:chemistry / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics*; D014161:Transduction, Genetic
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C451325:SbcE protein, Salmonella typhimurium; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli