rpos important sigma factor example

RpoS is

an alternative sigma factor in Escherichia coli that plays a central role in adaptation to suboptimal growth conditions.

growth,

not essential

controls

the expression of many genes that protect the cell from stress and help it scavenge nutrients.

The RpoS regulon is ,

variable

RpoS controls many genetic systems, including those affecting

pathogenesis,

phenotypic traits ( metabolic pathways and biofilm formation, the expression of genes needed to survive nutrient deprivation.)

• Function: RpoS

• helps E. coli adapt to changing conditions, (nutrient deprivation, osmotic stress, oxidative stress, and acid stress. )

• global regulator

• controls a large number of genes.

  • important in the transition to stationary phase.

• Evolution: RpoS likely arose from

• a duplication of the RpoD gene

• prior to the emergence of the Proteobacteria.

• It is found only in the Proteobacteria.

• The RpoS regulon is

• plastic

  • has adapted to the niche-specific needs of different bacteria.

• Regulation:

  • RpoS levels are

• low in exponential phase

  • increase as cells enter stationary phase.

• RpoS function is modulated by factors such as

• small RNAs,

• proteolysis,

  • interactions with other proteins.

• It also works with the small Crl protein to

• modulate RpoS regulon expression.

• The Crl protein is conserved within and restricted to the

• GammaProteobacteria.

• RpoS Regulon: The RpoS regulon includes hundreds of genes that require a large metabolic commitment.

• RpoS directly controls over 1000 genes in E. coli, with about two-thirds being positively controlled and the remainder being negatively controlled.

• Many genes are organized in operons or indirectly controlled.

• The number of promoters directly recognized by RpoS is much lower than the total number of genes it controls.

  • RpoS promoters can be classified as sensitive or insensitive to activation during adaptation to stationary phase.

• Negative Regulation: RpoS can have a negative regulatory role through

• sigma factor competition for core polymerase

• through RpoS/RpoD competition for stationary phase promoters.

  • Entire genetic pathways/systems are negatively controlled in E. coli. (TCA cycle, flagellar biosynthesis, and cryptic prophage genes)

• RpoS and Metabolism:

• RpoS may be a central regulator in a stress-vs.-nutrition paradigm.

• allows the cell to allocate resources to counter stress

• through selection for loss of RpoS function mutations,

• enable the cell to utilize an expanded range of substrates.

• Loss of RpoS function can lead to improved nutrient scavenging.

  • RpoS mutants have a selective advantage in mixed culture.

• RpoS Variability:

• RpoS levels are heterogeneous among single cells in a population, suggesting that

• stochastic variation may be an important determinant in generating subpopulations of cells.

• RpoS can be highly polymorphic in

• environmental isolates,

• loss of RpoS can be experimentally selected in

• pathogenic E. coli.

• RpoS in Pathogenesis: RpoS is important for the pathogenesis of some E. coli strains. For example,

• in enterohemorrhagic E. coli O157:H7, RpoS controls key metabolic pathways important for intestinal colonization.

• RpoS also positively regulates several LEE-encoded elements, which are needed for .

• virulence

• RpoS regulation of biofilm production is

• positive in E. coli K12

  • negative in O157:H7 strains.

• RpoS and Stationary Phase:

  • During stationary phase adaptation, E. coli cells undergo

• morphological remodeling and become resistant to specific stresses.

• RpoS and Stationary Phase:

  • Transcription is altered by

• the displacement of the major housekeeping RpoD sigma factor by RpoS.

• RpoS and Stationary Phase:

  • The RpoS regulon is important for

• survival in stationary phase.

• RpoS and Laboratory Strains: Laboratory domestication of natural isolates may lead to

• the acquisition of rpoS attenuation mutations,