Gene Transcription

Sigma factors are global regulators of gene transcription and confer specificity on transcription initiation by recognizing specific promoter sequences of different genes (Ho and Coates, 1999). Primary sigma factors in the RNA polymerase holoenzyme recognize housekeeping genes during the log-phase growth. With changes in environmental factors, sigma factors in the holoenzyme and the transcriptional regulation of different genes, are replaced.

Many free-living gram-negative bacteria, during entry into the stationary-phase, express genes that induce cellular resistance to environmental stresses such as oxidative stress and osmotic stress (Schellhorn, Audia, Wei and Chang, 1998). RpoS, a conserved alternative sigma factor whose expression is controlled by many factors, itself controls the many genes required for stationary-phase adaptation.

The rpoS gene encodes for the alternative sigma factor RpoS and is required for survival of bacteria under starvation and stress conditions (Ibanez-Ruiz, Robbe-Saule, Hermant and Norel, 2000). In mice, it is also essential for Salmonella virulence. S. typhimurium responds to a variety of environmental stresses by accumulating rpoS

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enes dependent on RpoS. Many RpoS-dependent genes were growth-phase-dependent at lower levels, even in RpoS backgrounds, suggesting that other growth-phase-dependent regulatory mechanisms in addition to RpoS may control postexponential gene expression. The results suggest that many growth-phase-regulated functions in E. coli do not require RpoS for expression. RpoS regulon in Salmonella Ibanez-Ruiz, Robbe-Saule, Hermant, Labrude and Norel (2000) characterized the RpoS regulon in Salmonella by isolating 38 unique RpoS-activated lacZ gene fusions from a bank of Salmonella enterica serovar typhimurium mutants with random Tn5B21 mutations. All gene fusions were regulated by growth phase, and the dependence on RpoS varied from three-fold to 95-fold. DNA sequence analysis identified seven fusions that mapped to DNA regions in S. enterica serovar typhimurium that do not match to any known E. coli sequence, suggesting the composition of the RpoS regulon differs markedly in the two species. None of the insertion mutations in DNA regions common to both species affected Salmonella virulence in BALB/c mice. The results indicated that the ogt gene in Salmonella is regulated by RpoS in the stationary phase of growth in rich medium, su
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Some common words found in the essay are:
Ho Coates, Labrude Norel, Wei Chang, Curtiss Foster, Bearson Foster, C52 SL1344, Hermant Norel, Summary Sigma, RpoS RpoS-dependent, Robbe-Saule Norel, sigma factors, sigma factor, environmental stresses, wei chang 1998, ibanez-ruiz robbe-saule, rpos regulon, stationary phase, norel 2000, siga sigb, gene fusions, alternative sigma factor, enterica serovar typhimurium, audia wei chang, coates 1999, typhimurium mol microbiol,
Approximate Word count = 1224
Approximate Pages = 5 (250 words per page)

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