Two highly related regulatory proteins, Shigella flexneri VirF and enterotoxigenic Escherichia coli Rns, have common and distinct regulatory properties

Abstract

The Rns protein of enterotoxigenic Escherichia coli (ETEC) and the VirF protein of Shigella flexneri are members of the AraC family of transcription regulators. Rns is required for positive activation of the CS1 fimbrial genes, while VirF is a positive regulator of an invasion gene regulon. The amino acid sequences of the proteins are 36% identical, and both proteins activate transcription in response to increases in temperature. Here, we show that Rns is capable of complementing fully a null mutation in the S. flexneri virF gene. However, the VirF protein cannot replace Rns as an activator of CS1 gene expression in ETEC. This failure is not due to the absence from ETEC of a co-factor required by VirF since it also occurs when the CS1 system is moved into an S. flexneri genetic background. Nor is it a function of growth medium composition or a failure in virF gene expression. Instead, these findings point to important differences in the mechanisms by which these related transcription factors regulate gene expression in Gram-negative pathogens. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.

In Vivo DNA-Binding and Oligomerization Properties of the Shigella flexneri AraC-Like Transcriptional Regulator VirF as Identified by Random and Site-Specific Mutagenesis

“…The virF ϩ plasmid pMEP31 was subjected to nitrosoguanidine mutagenesis (see Materials and Methods) and transformed into the S. flexneri virF mutant strain CJD1006. This strain exhibits a Lac Ϫ phenotype on indicator plates at 37°C due to the absence of the VirF activator; a Lac ϩ phenotype can be restored by introducing the virF gene on a multicopy plasmid (18). Three independent rounds of mutagenesis (Ϸ10,000 colonies screened) yielded 52 colonies with altered ␤-galactosidase activity on indicator plates.…”

“…Plasmid pMEP31 (17) is a derivative of pACYC184, in which the virF gene has been cloned onto a 7.9-kb BamHI fragment. The virF gene on a 1.3-kb HpaII fragment cloned into pACYC184 was designated pMEP510 (18), while the same fragment in pBR322 resulted in pMEP532. pACYC184-based plasmids harboring the same virF fragment as pMEP510 but with point mutations within the virF coding region were designated by the single-letter amino acid code of the mutation.…”

“…With one exception (UreR, which binds urea), the family members involved in virulence regulation do not bind specific effectors (6). Further evidence for common activation mechanisms among this subfamily is that some members, including VirF, can substitute for others in regulation of their cognate promoters (3,14,18,23).…”

Horizontal Transfer of CS1 Pilin Genes of EnterotoxigenicEscherichia coli

“…Rns is a member of the AraC family of transcription regulators (5). There is a group of homologous genes that are very closely related to rns that are also present in many enteric bacteria (6,7,12,34,38). Most similar (about 95% at the DNA level) are rns homologues found in many ETEC strains that do not produce CS1 pili.…”

“…These genes are often so closely related to rns that they are functionally interchangeable (7,34,38). Thus, if a recombinant pCoo plasmid entered a bacterium with one of these rns-related genes, these should also produce CS1 pili.…”