Transcriptional silencing and thermoregulation of gene expression in Escherichia coli

Abstract

Expression of specific adhesive properties by bacteria in general seems to be regulated to fit the environmental conditions. An example is the transcriptional regulation of digalactoside-specific binding by uropathogenic strains of Escherichia coli. The fimbrial structures (pili) on the bacterial surface carry the adhesin and are present during growth at 37 degrees C but are not produced by cells at lower temperatures, such as 25 degrees C. Thermoregulation of expression is due to temperature-dependent transcription of a regulatory cistron in the pilus-adhesin gene cluster. We have now identified and characterized a new regulatory locus (drdX) and show that a histone-like bacterial protein has an important role in this novel example of thermoregulation of transcription.

Self-perpetuating epigenetic pili switches in bacteria

“…Growth of E. coli in glucose reduces the OFF to ON switch rate by 35-fold as a result of lowered cAMP level, which prevents CAP-dependent activation of papBA and subsequent papI transcription (23). Pap pilin transcription is also significantly repressed by growth at low temperature (Ͻ26°C) (27,28) and rich medium (LB broth) (7). It is not clear whether these growth conditions directly alter the phase switch itself or alternatively inhibit pap transcription in phase ON cells.…”

“…However, this 15.5-kDa global regulatory protein does modulate Pap phase switching, and appears to play an essential role in the repression of Pap expression by environmental signals including low temperature (27). At temperatures below 26°C, H-NS appeared to bind to the pap regulatory region as evidenced by methylation protection of the two pap GATC sites (6).…”

“…It is not clear whether these growth conditions directly alter the phase switch itself or alternatively inhibit pap transcription in phase ON cells. The mechanism by which these conditions repress pap transcription is not known, but appears to involve H-NS because introduction of an hns mutation partially relieves repression (7,27).…”

Mutational Analysis of the PapB Transcriptional Regulator inEscherichia coli

“…It may act as a negative regulator of transcription (40,41), functioning by "transcriptional silencing" (42) and "repression via DNA topology" (41, 43) through oligomeric binding to DNA. Three putative functional domains have been identified in b Superinfection immunity (Imm.)…”

H‐NS: a modulator of environmentally regulated gene expression

“…However, the mechanism is not clear. There is no difference in the level of hns mRNA and therefore presumably no difference in the concentration of H-NS protein in the relevant temperature range (Gö ransson et al, 1990;Colonna et al, 1995;Sondé n and Uhlin, 1996). In Shigella flexneri, where the expression of the invasion regulatory gene, virB, at 30ЊC is less than 1/20th of that at 37ЊC, it has recently been shown that this thermoregulation is dependent on the superhelicity of the virB promoter and is not mediated by H-NS (Tobe et al, 1995).…”