In vivo recruitment analysis and a mutant strain without any group 2 σ factor reveal roles of different σ factors in cyanobacteria.
In eubacteria, replacement of one σ factor in the RNA polymerase (RNAP) holoenzyme by another one changes the transcription pattern. Cyanobacteria are eubacteria characterized by oxygenic photosynthesis, and they typically encode numerous group 2 σ factors that closely resemble the essential primary σ factor. A mutant strain of the model cyanobacterium Synechocystis sp. PCC 6803 without functional group 2 σ factors (named as ΔsigBCDE) could not acclimate to heat, high salt or bright light stress, but in standard conditions ΔsigBCDE grew only 9% slower than the control strain. One-fifth of the genes in ΔsigBCDE was differently expressed compared with the control strain in standard growth conditions and several physiological changes in photosynthesis, and pigment and lipid compositions were detected. To directly analyze the σ factor content of RNAP holoenzyme in vivo, a His-tag was added to the γ subunit of RNAP in Synechocystis and RNAPs were collected. The results revealed that all group 2 σ factors were recruited by RNAP in standard conditions, but recruitment of SigB and SigC increased in heat stress, SigD in bright light, SigE in darkness and SigB, SigC and SigE in high salt, explaining the poor acclimation of ΔsigBCDE to these stress conditions.
Department of Biochemistry, University of Turku, FIN-20014, Turku, Finland.
Satu
S
Koskinen
Department of Biochemistry, University of Turku, FIN-20014, Turku, Finland.
Kaisa
K
Hakkila
Department of Biochemistry, University of Turku, FIN-20014, Turku, Finland.
Liisa
L
Gunnelius
Department of Biochemistry, University of Turku, FIN-20014, Turku, Finland.
Juha
J
Kurkela
Department of Life Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, 153-8902, Japan.
Hajime
H
Wada
Department of Biochemistry, University of Turku, FIN-20014, Turku, Finland.
Taina
T
Tyystjärvi
D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D006358:Hot Temperature; D008027:Light; D050356:Lipid Metabolism; D010788:Photosynthesis; D010860:Pigments, Biological / Q000378:metabolism; D012808:Sigma Factor / Q000378:metabolism*; D013312:Stress, Physiological; D046939:Synechocystis / Q000235:genetics* / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects
D010860:Pigments, Biological; D012808:Sigma Factor; D012321:DNA-Directed RNA Polymerases