title: Genetic analysis of the phase variation control of expression of type 1 fimbriae in Escherichia coli.
abstract: Expression of type 1 fimbriae in Escherichia coli exhibits phase variation, whereby individual cells can alternate between states of organelle expression (Fim+) and nonexpression (Fim-). Strains with a fimD-lac operon fusion, in which lac, rather than fimD, expression is under the control of the fimD promoter, undergo Lac+ in equilibrium Lac- phase variation, instead. After positioning a lambda prophage adjacent to the operon fusion, we were able to isolate specialized lambda phage carrying both the fimD-lac fusion and the phase variation control region. Introduction of such phage into an Fim+ strain resulted in construction of a strain with a double, independently switching phenotype (Fim+ in equilibrium Fim- and Lac+ in equilibrium Lac-), demonstrating that the region controlling phase variation is contiguous with the fimD-lac operon fusion and is cis acting. When the specialized lambda phage was propagated on a delta lac delta fim strain, phase variation occurred within the plaques, confirming that the phase variation control region is carried on the specialized transducing phage. All lysogens acquired the Lac+ in equilibrium Lac- phenotype, except for two nonswitching Lac+ recombinants, which acquired Lac+ in equilibrium Lac- phase variation only by trans complementation with fim. Phase variation of type 1 fimbriae, therefore, appears to involve both a cis-active element, which is cloned on a specialized lambda phage, and a trans-active permissive factor, which is not present on the phage, but rather must be supplied by the recipient strain in the transduction.
authors.forename: C S
authors.initials: CS
authors.lastname: Freitag
authors.forename: J M
authors.initials: JM
authors.lastname: Abraham
authors.forename: J R
authors.initials: JR
authors.lastname: Clements
authors.forename: B I
authors.initials: BI
authors.lastname: Eisenstein
mesh_terms: D004926:Escherichia coli / Q000235:genetics*; D010861:Fimbriae, Bacterial; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D005809:Genes, Regulator; D006579:Heterozygote; D007763:Lac Operon