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The ω subunit of RNA polymerase is essential for thermal acclimation of the Cyanobacterium Synechocystis sp. PCC 6803

ABSTRACT: The rpoZ gene encodes the small ω subunit of RNA polymerase (RNAP). A ∆rpoZ strain of the cyanobacterium Synechocystis sp. PCC 6803 grew well in standard conditions (constant illumination at 40 µmol photons m-2s-1; 32 °C; ambient CO2) but was heat sensitive and died at 40 °C. In the control strain , 71 genes were at least two-fold up-regulated and 91 genes down-regulated after a 24-h treatment at 40 °C, while in ∆rpoZ 394 genes responded to heat. Only 62 of these heat-responsive genes were similarly regulated in both strains, and 80 % of heat-responsive genes were unique for ΔrpoZ. The RNAP core and the primary σ factor SigA were down-regulated in control strain at 40 °C, but not in ΔrpoZ. In accordance with reduced RNAP content, the total RNA content of mild-heat-stress-treated cells was lower in control strain than in ΔrpoZ. Light-saturated photosynthetic activity decreased more in ΔrpoZ than in control strain upon mild heat stress. The amounts of Photosystem II and Rubisco decreased at 40 °C in both strains while PSI and the phycobilisome antenna protein allophycocyanin remained at the same level as in standard conditions. The phycobilisome rod proteins, phycocyanins, diminished during the heat treatment in ΔrpoZ but not in control strain, and the nblA1 and nblA2 genes (encode NblA proteins required for phycobilisome degradation) were up-regulated only in ΔrpoZ. Our results show that the ω subunit of RNAP is essential in heat stress because it is required for heat acclimation of diverse cellular processes.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE59451 | GEO | 2014/11/11

SECONDARY ACCESSION(S): PRJNA255362

REPOSITORIES: GEO

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Project description:When performed at single bp resolution, the genome-wide location, occupancy level, and structural organization of DNA binding proteins provides mechanistic insights into genome regulation. Here we use ChIP-exo to provide the first high resolution view of the epigenomic organization of the E. coli transcription machinery and nucleoid structural proteins when cells are growing exponentially and upon rapid reprogramming (acute heat shock). We suggest that indirect readout of DNA shape at the flanks of cognate motifs provide major contributions to site specificity at promoter positions -35/-24 and -10/-12. We examined the site specificity of three sigma factors (RpoD/70, RpoH/32, and RpoN/54), RNA polymerase (RNAP or RpoA, B, C) and two nucleoid proteins (Fis and IHF). Our results confirm and refine reports that RpoD binds most annotated promoters, whereas RpoH and RpoN bind a much smaller subset, each through their cognate motifs. However, only upon heat shock does RpoH becomes active for RNAP recruitment. In contrast, upon heat shock RpoD remains active at its cognate promoters (including at heat shock genes), whereas RpoN remains inactive at its cognate promoters. RpoN binds ~1,000 non-annotated RpoN motifs, which may reflect a large number of condition-specific transcription units. Occupancy patterns of sigma factors and RNAP suggest a common promoter recruitment mechanism that differs from the long-standing views that sigma and RNAP are co-recruited as a complex, and also simultaneously dissociate from promoters. Our findings suggest that sigma factors are recruited and/or maintained at most promoters via an RNAP-independent mechanism. When RNAP arrives, it dwells for a relatively short time before clearing the promoter, leaving sigma behind. Taken together these findings add new dimensions to how sigma factors achieve promoter specificity through DNA sequence and shape and redefine mechanistic steps in regulated promoter assembly in E. coli.

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The ω subunit of RNA polymerase is essential for thermal acclimation of the Cyanobacterium Synechocystis sp. PCC 6803

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