The Rhodobacter sphaeroides ECF sigma factor, sigma(E), and the target promoters cycA P3 and rpoE P1.
Rhodobacter sphaeroides rpoE encodes a 19.2 kDa protein, sigma(E), related to members of the extra-cytoplasmic function subfamily of eubacterial RNA polymerase sigma factors. We demonstrate that sigma(E) directs transcription from rpoE P1, the promoter for the rpoEchrR operon, and from cycA P3, a promoter for the cytochrome c2 structural gene. Comparison of these sigma(E)-dependent promoters reveals significant sequence conservation in their -35 and -10 regions; however, rpoE P1 is over 80-fold stronger than cycA P3. Both promoters contain identical -35 hexamers, (-36)TGATCC(-31), that appear to constitute the preferred sequence, since any single base mutation in this region of cycA P3 reduces promoter function. The higher activity of rpoE P1 appears to reflect a better -10 region, (-13)TAAGA(-9), as it contains four out of five of the nucleotides found to be important to sigma(E)-dependent transcription. We also propose that ChrR acts as an inhibitor of sigma(E), since these two proteins can form a complex, and DeltachrR mutations increase sigma(E)-dependent transcription. ChrR is believed to respond to a signal from tetrapyrrole biosynthesis because loss of function mutations in chrR lead to cohemin resistance. Based on our observations, we present a model in which cohemin resistance is conferred by increasing sigma(E) activity.
Newman
J D
JD
Department of Bacteriology, University of Wisconsin Madison, Madison, WI 53706, USA.
Falkowski
M J
MJ
Schilke
B A
BA
Anthony
L C
LC
Donohue
T J
TJ
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003574:Cytochrome c Group / Q000235:genetics*; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D004252:DNA Mutational Analysis; D004352:Drug Resistance, Microbial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006418:Heme / Q000494:pharmacology; D006427:Hemin; D006639:Histidine / Q000235:genetics; D008969:Molecular Sequence Data; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012242:Rhodobacter sphaeroides / Q000187:drug effects / Q000235:genetics*; D012808:Sigma Factor / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D001426:Bacterial Proteins; C093117:ChrR protein, Rhodobacter sphaeroides; D003574:Cytochrome c Group; D012808:Sigma Factor; D014157:Transcription Factors; C063202:sporulation-specific sigma factors; D006418:Heme; D006639:Histidine; D006427:Hemin; C017165:cytochrome c(3)