Phase variation of type 1 fimbriation in Escherichia coli is associated with the inversion of a 314-bp DNA element, positioned proximal to and upstream of fimA, which encodes the major type 1 fimbrial subunit. This DNA switch region contains a promoter that drives transcription of fimA only when the switch is in the ON orientation. Using chromosomal and plasmid-borne lacZ reporter cassettes, we show here how the global regulator H-NS affects the activity of the fimA promoter. In phase-locked reporter cassettes the activity of the fimA promoter was found to be enhanced in a hns-positive background, but only when the switch was in the ON orientation. Also, the number of fimbriae produced by a phase-locked ON strain was significantly higher in a hns-positive background. By means of competitive gel retardation and DNase I protection assays, H-NS binding to DNA segments adjacent to and within the phase switch region was demonstrated.
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Received: 14 January 1998 / Accepted: 25 May 1998
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Schembri, M., Olsen, P. & Klemm, P. Orientation-dependent enhancement by H-NS of the activity of the type 1 fimbrial phase switch promoter in Escherichia coli . Mol Gen Genet 259, 336–344 (1998). https://doi.org/10.1007/s004380050820
- Key wordsfimA promoter
- H-NS binding
- Expression enhancement
- Type 1 fimbriae