Localization of promoters in the fim gene cluster and the effect of H-NS on the transcription of fimB and fimE.

The expression of type 1 fimbriae in Escherichia coli undergoes phase variation in which individual bacteria switch between a fimbriated and non-fimbriated state. The transition from one state to the other is caused by inversion of a DNA segment containing the promoter for the fimA gene. The orientation of the invertible segment is controlled by two proteins, FimB and FimE, which mediate an on/off and off only orientation of the segment, respectively. In this study we have mapped the 5' termini of the fimB, fimE and fimA transcripts. Furthermore, we show that expression of fimB and fimE is strongly influenced by the H-NS nucleoid protein.