The EMBO Journal Vol. 19,pp. 1450-1457, 2000, Copyright © European Molecular Biology Organization

Regulatory cross-talk between adhesin operons in Escherichia coli: inhibition of type 1 fimbriae expression by the PapB protein

Yan Xia, David Gally, Kristina Forsman-Semb¹ and Bernt Eric Uhlin¹

¹ Department of Microbiology, Umeå University, S-90187 Umeå, Sweden and ² Zoonotic and Animal Pathogens Research Laboratories, Department of Veterinary Pathology, Medical Microbiology, Teviot Place, The University of Edinburgh, Edinburgh EH8 9AG, UK
³   Present address: AstraZeneca, Molecular Biology, S-43183 Mölndal, Sweden
⁴   Corresponding author
   e-mail: bernt.eric.uhlin{at}micro.umu.se

Pathogenic Escherichia coli often carry determinants for several different adhesins. We show a direct communication between two adhesin gene clusters in uropathogenic E.coli: type 1 fimbriae (fim) and pyelonephritis-associated pili (pap). A regulator of pap, PapB, is a key factor in this cross-talk. FimB recombinase turns on type 1 fimbrial expression, and PapB inhibited phase transition by FimB in both off-to-on and on-to-off directions. On-to-off switching requiring FimE was increased by PapB. By analysis of FimB- and FimE-LacZ translational fusions it was concluded that the increase in on-to-off transition rates was via an increase in FimE expression. Inhibition of FimB-promoted switching was via a different mechanism: PapB inhibited FimB-promoted in vitro recombination, indicating that FimB activity was blocked at the fim switch. In vitro analyses showed that PapB bound to several DNA regions of the type 1 fimbrial operon, including the fim switch region. These data show that Pap expression turns off type 1 fimbriae expression in the same cell. Such cross-talk between adhesin gene clusters may bring about appropriate expression at the single cell level.