Induction of a Group 2 σ Factor, RPOD3, by High Light and the Underlying Mechanism in Synechococcus elongatus PCC 7942

Abstract

Among the 70 family bacterial factors, group 2 factors have similar promoter recognition specificity to group 1 (principal) factors and express and function under specific environmental and physiological conditions. In general, the cyanobacterial genome encodes more than four group 2 factors, and the unicellular Synechococcus elongatus PCC 7942 (Synechococcus) has five group 2 factors (RpoD2-6). In this study, we analyzed expression of group 2 factors of Synechococcus at both mRNA and protein levels, and we showed that the rpoD3 expression was activated only by high light (1,500 mol photons m ؊2 s ؊1 ) among the various stress conditions examined. After high light shift, rpoD3 mRNA accumulated transiently within the first 5 min and diminished subsequently, whereas RpoD3 protein increased gradually during the first several hours. We also found that the rpoD3 deletion mutant rapidly lost viability under the same conditions. Analysis of the rpoD3 promoter structure revealed the presence of an HLR1 (high light-responsive element 1) sequence, which was suggested to be responsible

Cross-talk and regulatory interactions between the essential response regulator RpaB and cyanobacterial circadian clock output

“…Our results suggest that overexpressed RpaB receiver affects phenotypes such as altered cell dimensions, or the previously described induction of RpaB-repressed targets, such as hliA and rpoD3 (19), by a mechanism other than by decreasing the RpaB∼P/RpaB ratio , or RpaB N-ter on the rhythmic expression of kaiBC and purF. Bioluminescence activity of P kaiBC ::luc or P purF ::luc reporters was assayed in the WT (A and B), cikA (C and D), and rpaA (E and F) genetic backgrounds.…”

NblR Is a Novel One-Component Response Regulator in the CyanobacteriumSynechococcus elongatusPCC 7942

“…Under stress conditions, dissociation of RpaB from HLR1 resulted in transient expression of hliA and rpoD3. 30) Together, these results suggest that RpaB, not NblR, is the cognate response regulator of NblS that might repress nblA transcription via HLR1, and that SipA also has the repressive function of mediating the signal-transduction pathway between NblS and RpaB. Therefore, under normal conditions, expression of nblA can be repressed by the above-mentioned NblS-(SipA)-RpaB system, and, upon stress such as nutrient deprivation, a positive regulator of NblR that enhances nblA transcription might be activated by an as yet unknown mechanism.…”

RpaB, Another Response Regulator Operating Circadian Clock-dependent Transcriptional Regulation in Synechococcus elongatus PCC 7942

“…For expression of RpaA or RpaB with three copies of the FLAG epitope tag at their COOH termini, a recombinant plasmid described previously (18,19) was introduced into the NUC 42 strain to yield strains designated RAF and RBF, respectively. Synechococcus cells were grown in BG-11 medium (20) and in a continuous culture system (optical density at 730 nm of ϳ0.3) at 30°C under light at an intensity of ϳ40 mol m Ϫ2 s Ϫ1 .…”