title: Campylobacter fetus sap inversion occurs in the absence of RecA function.
abstract: Phase variation of Campylobacter fetus surface layer proteins (SLPs) occurs by inversion of a 6.2-kb DNA segment containing the unique sap promoter, permitting expression of a single SLP-encoding gene. Previous work has shown that the C. fetus sap inversion system is RecA dependent. When we challenged a pregnant ewe with a recA mutant of wild-type C. fetus (strain 97-211) that expressed the 97-kDa SLP, 15 of the 16 ovine-passaged isolates expressed the 97-kDa protein. However, one strain (97-209) expressed a 127-kDa SLP, suggesting that chromosomal rearrangement may have occurred to enable SLP switching. Lack of RecA function in strains 97-211 and 97-209 was confirmed by their sensitivity to the DNA-damaging agent methyl methanesulfonate. Southern hybridization and PCR of these strains indicated that the aphA insertion into recA was stably present. However, Southern hybridizations demonstrated that in strain 97-209 inversion had occurred in the sap locus. PCR data confirmed inversion of the 6.2-kb DNA element and indicated that in these recA mutants the sap inversion frequency is reduced by 2 to 3 log(10) units compared to that in the wild type. Thus, although the major sap inversion pathway in C. fetus is RecA dependent, alternative lower-frequency, RecA-independent inversion mechanisms exist.
authors.affiliation: Vanderbilt University School of Medicine and VA Medical Center, Nashville, Tennessee, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Ray
authors.forename: Z C
authors.initials: ZC
authors.lastname: Tu
authors.forename: R
authors.initials: R
authors.lastname: Grogono-Thomas
authors.forename: D G
authors.initials: DG
authors.lastname: Newell
authors.forename: S A
authors.initials: SA
authors.lastname: Thompson
authors.forename: M J
authors.initials: MJ
authors.lastname: Blaser
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D015139:Blotting, Southern; D002168:Campylobacter fetus / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D007446:Chromosome Inversion; D004269:DNA, Bacterial / Q000235:genetics*; D005260:Female; D008562:Membrane Glycoproteins; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D009153:Mutagens / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism*; D011995:Recombination, Genetic; D012756:Sheep
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008562:Membrane Glycoproteins; D009153:Mutagens; C055764:S-layer proteins; D008741:Methyl Methanesulfonate; D011938:Rec A Recombinases