Induction of a group 2 sigma factor, RPOD3, by high light and the underlying mechanism in Synechococcus elongatus PCC 7942.
Among the sigma70 family bacterial sigma factors, group 2 sigma factors have similar promoter recognition specificity to group 1 (principal) sigma factors and express and function under specific environmental and physiological conditions. In general, the cyanobacterial genome encodes more than four group 2 sigma factors, and the unicellular Synechococcus elongatus PCC 7942 (Synechococcus) has five group 2 sigma factors (RpoD2-6). In this study, we analyzed expression of group 2 sigma factors of Synechococcus at both mRNA and protein levels, and we showed that the rpoD3 expression was activated only by high light (1,500 micromol 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 for the high light-induced transcription under the control of the NblS (histidine kinase)-RpaB (response regulator) two-component system (Kappell, A. D., and van Waasbergen, L. G. (2007) Arch. Microbiol. 187, 337-342), at +6 to +23 with respect to the transcriptional start site. Here we demonstrated that recombinant RpaB protein specifically bound to HLR1 of the rpoD3 and hliA genes in vitro, and overexpression of a truncated RpaB variant harboring only the phosphoreceiver domain derepressed the transcription in vivo. Thus, we have concluded that phosphorylated RpaB are repressing the rpoD3 and hliA transcription under normal growth conditions, and the RpaB dephosphorylation induced by high light stress results in transcriptional derepression.
Seki
Asako
A
Institute of Molecular and Cellular Biosciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Hanaoka
Mitsumasa
M
Akimoto
Yuki
Y
Masuda
Susumu
S
Iwasaki
Hideo
H
Tanaka
Kan
K
D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000096:biosynthesis* / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology / Q000528:radiation effects*; D016680:Genome, Bacterial / Q000502:physiology*; D000071677:Histidine Kinase; D008027:Light; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020218:Response Elements / Q000502:physiology; D012808:Sigma Factor / Q000096:biosynthesis* / Q000235:genetics; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology / Q000528:radiation effects
D001426:Bacterial Proteins; D012333:RNA, Messenger; D012808:Sigma Factor; D014157:Transcription Factors; D011494:Protein Kinases; D000071677:Histidine Kinase; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases