Bacterial Stress Responses Bacterial Stress Responses General stress
第七章 细菌应激反应 Bacterial Stress Responses
Bacterial Stress Responses Ø General stress response Activation of Rpo. S (σ38) by cessation of growth Induction of Pol IV, error prone polymerase Ø Heat-shock response Activation of Rpo. H (σ32), induction of Gro. E protects Pol V from degradation Ø Stringent response Amino acid deprivation, starvation Mediated by guanosine tetraphosphate, pp. Gpp Enhances Rpo. H and Rpo. S responses Ø SOS response Triggered by damage to DNA Lex. A-Rec. A mediated
• 1975年O’Farrell 2 D研究E. coli heat-shock proteins, 2003年Hatfield用microarray研究应激反 应. • 基因表达-转录, 转录后调控, 细菌中转录调控为主. • DNA-dependent RNA polymerase, (five subunits a 2 bb’w) 和an additional subunit (σ). E. coli有7个 sigma factors: σ 70 and the vegetative sigma factors, Rpo. D, Rpo. N, Rpo. S, Rpo. H, Rpo. F, Rpo. E, and Fec. I. 这些σ因子通�� 争和RNase 核心酶� 合, ���� 控起主要租用, 另外�� 抑 制因子, 激活因子, σ� 合因子, 抗σ因子, 以及一些 小RNAs的� 控起� 助作用.
Regulation of Rpo. S Expression • Rpo. S is induced during the transition from exponential phase to stationary phase or in response to various stress conditions, 引起 细胞生理和形态的改变 • Rpo. S的表达受严格控制at the transcriptional, translational, and posttranslational levels
nlp. D Fis, a global transcriptional factor, inhibits rpo. S transcription by directly binding to the rpo. S promoter region. Fis levels are growth-phase dependent. At the onset of stationary phase, Fis disappears and the transcription of rpo. S is induced
Model for the mechanism of action of Rss. B in regulating S degradation by Clp. XP.
Rpo. S, a Master Regulator in Stress Response and Adaptation • More than 10% of the E. coli genome is controlled by Rpo. S, most of which is involved in stress response, such as nutrient limitation resistance to DNA damage, osmotic shock high hydrostatic pressure, oxidative stress, ethanol resistance, adaptive mutagenesis, acid stress, and biofilm formation. • Rpo. S controls a more degenerate promoter sequence featuring a − 10 region (TAYACT),
Heat-shock response • In E. coli heat-shock induces pproximately 30 genes under control of another sigma factor, Rpo. H (32). • The Rpo. H-regulon is also induced by unfolded proteins • Levels of DNA Pol V are dependent on Gro. E because the chaperon interacts with the polymerase subunit of Pol. V and protects it from degradation • The gro. EL/ES operon, which encodes the molecular chaperone Gro. E, is an important member of this regulon.
Heat-shock response in bacteria • heat-shock responsive genes have specific sequences in their promoters which replace the common -35 and -10 regions: • • these promoters are recognized byσ32 is encoded by the rpo. H gene. The m. RNA is stabilized by heat-shock leading to increased translation. • In E. coli heat-shock induces approximately 30 genes under control of another sigma factor, Rpo. H.
Heat Shock Response in Eukaryotes • also have specific sequences, in this case upstream of heat-shock genes - HSE (Heat Shock Element) • This is bound by (HSF) Heat Shock Factor, trimerizes using a leucine zipper. • HSF is phosphorylated as a consequence of heat shock - this activates it and allows transcription to take place from the promoter
σ32(Rpo. H), the heat shock sigma factor, is rapidly degradedunder normal growth conditions by the AAA protease, Fts. H, in a reaction modulated by the Dna. J/Dna. K/Grp. E chaperone system. During heat shock, 32 is transiently stabilized, and this stabilization results in the rapid increase in the synthesis of the heat shock proteins (Yura and Nakahigashi 1999).
SOS反应 When bacteria are subjected to DNA damage about 30 genes are coordinately induced, a reaction known as the “SOS response”. SOS genes may be induced to some degree under a variety of stressful conditions
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