Involvement of FIS in the H-NS-mediated regulation of virF gene of Shigella and enteroinvasive Escherichia coli

Falconi, M Prosseda, G Giangrossi, M Beghetto, E Colonna, B

M. Falconi et al., Involvement of FIS in the H-NS-mediated regulation of virF gene of Shigella and enteroinvasive Escherichia coli, MOL MICROB, 42(2), 2001, pp. 439-452

54

INGLESE

Article

Microbiology

MOLECULAR MICROBIOLOGY

0950-382X → ACNP

42

2

2001

439 - 452

ISI

0950-382X(200110)42:2<439:IOFITH>2.0.ZU;2-R

The mechanism of pathogenicity in Shigella and enteroinvasive Escherichia c oli (EIEC) requires the co-ordinated expression of several genes located on both the virulence plasmid and the chromosome. We found that cells lacking a functional FIS protein (factor for inversion stimulation) are partially impaired in expressing the virulence genes and that full expression is tota lly restored when Shigella wildtype fis gene is offered in trans. We also i dentified virF, among the virulence genes, as a target of FIS-mediated acti vation and showed that FIS binds to four specific sites in the promoter reg ion of virF. Previous studies have demonstrated that the expression of VirF , the first positive activator of a multistep regulatory cascade, is subjec t to temperature-dependent regulation by H-NS, one of the main nucleoid-ass ociated proteins. We now demonstrate that two of the four FIS sites overlap one of the two H-NS sites responsible for thermoregulation (H-NS site I). FIS was found to exercise a direct positive transcriptional control at perm issive temperature (37 degreesC), when H-NS fails to repress virF, as well as an indirect effect by partially counteracting H-NS inhibition at the tra nsition temperature (32 degreesC). Our data indicate that FIS may be releva nt for the rapid increase in virF expression after penetration of bacteria into the host.