Inactivation of group 2 σ factors upregulates production of transcription and translation machineries in the cyanobacterium Synechocystis sp. PCC 6803.

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.