MULTICOPY FIMB GENE-EXPRESSION IN ESCHERICHIA-COLI - BINDING TO INVERTED REPEATS IN-VIVO, EFFECT ON FIMA GENE-TRANSCRIPTION AND DNA INVERSION

Transcription of fimA, the Escherichia coil gene encoding the type 1 f imbrial subunit protein, is driven by a promoter carried on a 314 bp s egment of invertible DNA. We have discovered that overexpression of fi mB, one of the genes required for inversion of this DNA element, resul ts in transcriptional repression of fimA. Furthermore, under these con ditions inversion ceases to be dependent on the integration host facto r (IHF) or the leucine-responsive regulatory protein (LRP), cofactors hitherto considered to be essential for inversion. Inversion will even occur (albeit at a very low level) in the absence of both cofactors, The interaction of the fimB gene product with the invertible element w as studied in vivo in the presence of single- and multicopy fimB genes , Dimethyl sulphoxide (DMS)-mediated methylation of DNA at the 9 bp in verted repeats, which flank the invertible element, was found to vary in the presence and absence of functional fimB. The DMS reactivity pro file at the left-hand inverted repeat was similar with single or multi copy fimB. The corresponding profile at the right-hand inverted repeat varied with fimB copy number. As this repeat lies between the fimA pr omoter and open reading frame, FimB binding here is likely to modulate fimA transcription and vice versa.