Abstract
We show that the formation of the RNAP holoenzyme with the primary σ factor SigA increases in the ΔsigBCDE strain of the cyanobacterium Synechocystis sp. PCC 6803 lacking all group 2 σ factors. The high RNAP-SigA holoenzyme content directly induces transcription of a particular set of housekeeping genes, including ones encoding transcription and translation machineries. In accordance with upregulated transcripts, ΔsigBCDE contain more RNAPs and ribosomal subunits than the control strain. Extra RNAPs are fully active, and the RNA content of ΔsigBCDE cells is almost tripled compared to that in the control strain. Although ΔsigBCDE cells produce extra rRNAs and ribosomal proteins, functional extra ribosomes are not formed, and translation activity and protein content remained similar in ΔsigBCDE as in the control strain. The arrangement of the RNA polymerase core genes together with the ribosomal protein genes might play a role in the co-regulation of transcription and translation machineries. Sequence logos were constructed to compare promoters of those housekeeping genes that directly react to the RNAP-SigA holoenzyme content and those ones that do not. Cyanobacterial strains with engineered transcription and translation machineries might provide solutions for construction of highly efficient production platforms for biotechnical applications in the future.
Highlights
Cyanobacteria are eubacteria characterized by oxygenic photosynthesis
The small ω subunit of RNA polymerase (RNAP) is non-essential in cyanobacteria just like in many other eubacteria[6], and it might play a regulatory role in cyanobacteria[7]
This competition is affected by numerous factors including the amount of each σ factor, affinity of different σ factors to the RNAP core, amounts and activities of anti-σ factors that prevent recruitment of a particular σ factor, and RNAP modifying factors like the small signaling molecule ppGpp that directly binds to the RNAP core and changes the recruitment efficiency of different σ factors and affect the promoter selectivity of the RNAP holoenzyme[8,9,10]
Summary
Cyanobacteria are eubacteria characterized by oxygenic photosynthesis. They branched early from other eubacteria and are currently found where ever light is available, from oceans to hot springs and fresh water environments to desert crust. This competition is affected by numerous factors including the amount of each σ factor, affinity of different σ factors to the RNAP core, amounts and activities of anti-σ factors that prevent recruitment of a particular σ factor, and RNAP modifying factors like the small signaling molecule ppGpp that directly binds to the RNAP core and changes the recruitment efficiency of different σ factors and affect the promoter selectivity of the RNAP holoenzyme[8,9,10] These processes are not yet well understood in cyanobacteria. Numerous RNAP-SigA holoenzymes enhance the transcription of a particular set of housekeeping genes including those encoding transcription and translation machineries, and ΔsigBCDE produces more RNAPs and ribosomal subunits than the control strain. The extra RNAPs are fully functional, and enhanced transcription leads to a high RNA content per cell whereas extra ribosomal subunits do not form translationally active ribosomes, and ΔsigBCDE cells show similar translation activity and protein content as the control strain. Co-regulation of transcription and translation machineries as well as promoter differences between subgroups of housekeeping genes will be discussed
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