Distant cis‐active sequences and sialic acid control the expression of fimB in Escherichia coli K‐12

Abstract

SummaryThe phase variation of type 1 fimbriation in Escherichia coli is controlled by the inversion of a 314 bp element of DNA, determined by FimB (switching in both directions) or FimE (switching from the ON-to-OFF orientation predominantly), and influenced by auxiliary factors IHF, Lrp and H-NS. The fimB gene is separated from the divergently transcribed yjhATS operon by a large (1.4 kbp) intergenic region of unknown function. Here, we show that fimB expression is regulated by multiple cis-active sequences that lie far upstream ( > 600 bp) of the transcription start sites for the recombinase gene. Two regions characterized further (regions 1 and 2) show sequence identity, and each coincides with a methylation-protected Dam (5 ¢ ¢ ¢ ¢ -GATC) site. Regions 1 and 2 apparently control fimB expression by an antirepression mechanism that involves additional sequences proximal to yjhA . Region 1 encompasses a 27 bp DNA sequence conserved upstream of genes known ( nanAT ) or suspected ( yjhBC ) to be involved in sialic acid metabolism, and we show that FimB expression and recombination are suppressed by Nacetylneuraminic acid. We propose that E. coli recognizes the amino sugars as a harbinger of potential host defence activation, and suppresses the expression of type 1 fimbriae in response.

Function and Expression of an N -Acetylneuraminic Acid-Inducible Outer Membrane Channel in Escherichia coli

“…GlcNAc-6-P is further metabolized to fructose-6-phosphate by NagA and NagB, two enzymes of the N-acetylglucosamine (GlcNAc) degradation pathway, whose synthesis is controlled by the nagC-encoded repressor (10,20). Neu5Ac regulates transcription of fimB, and it has been suggested that it could also control the expression of the divergently expressed yjhATS operon (7,29). We show in this work that yjhA is indeed regulated by NanR and several other regulators and that it encodes a Neu5Ac-specific channel.…”

“…fimB expression is regulated by Neu5Ac through the binding of the NanR regulator at a specific site in the fimB-yjhA intergenic region (Fig. 1A) (7,27). To verify whether NanR could also control yjhA expression, we measured expression of a yjhA-lacZ fusion in the absence and presence of Neu5Ac.…”

“…The function of YjhT and YjhS is not known, and they have no homology with proteins of known function. This operon is transcribed divergently from fimB, a gene whose product catalyzes the site-specific inversion of the region controlling transcription of the fimbrial structure genes (fimA to fimH) (7). The intergenic yjhA-fimB region is exceptionally large for E. coli (1.4 kb).…”

Integrated regulatory responses of fimB to N -acetylneuraminic (sialic) acid and GlcNAc in Escherichia coli K-12

“…Phase variation of fim is associated with inversion of a short (Ϸ300 bp) DNA element that contains a promoter for the structural genes (18,19). Inversion of the fim element involves two tyrosine family recombinase proteins, FimB and FimE, and is subject to elaborate control producing both (i) a relatively low frequency of switching from the afimbriate (off) to fimbriate (on) phase (between 10 Ϫ4 and 10 Ϫ3 per cell per generation), and (ii) control by environmental signals, including temperature, the branched-chain amino acids (particularly leucine) and alanine, and Neu 5 Ac (20)(21)(22). Whereas the amino acids stimulate fim phase variation in both directions, Neu 5 Ac inhibits switching from the off to on phase specifically (21,22).…”

“…Whereas the amino acids stimulate fim phase variation in both directions, Neu 5 Ac inhibits switching from the off to on phase specifically (21,22). Neu 5 Ac inhibits fimB expression, and thus exerts a selective effect on the inversion by inhibiting FimB, but not FimE, recombination (21).…”