The rpoD gene encoding the principal sigma factor (sigma(70)) of Pseudomona
s aeruginosa is transcribed from two promoters, P-C and P-HS The sequence o
f P-C is similar to the Escherichia coli sigma(70) consensus promoter seque
nce and that of P-HS is similar to the E. coil sigma(H) consensus promoter
sequence. Synthesis of rpoD mRNA from P-C is constitutive under both steady
-state and heat-shock growth conditions, while that of PHS is transiently i
nduced upon heat-shock. To gain a better understanding of the regulation of
r(POD) expression, we examined in vitro transcription of rpoD using two RN
A polymerases (E sigma(70) and E sigma(H), containing sigma(70) and sigma(H
), respectively) purified from P. aeruginosa. DNase I footprinting analysis
showed specific bindings of E sigma(70) and E sigma(H) to P-C and P-HS pro
moter regions, respectively. In the in vitro runoff transcription assay, E
sigma(H) transcribed the template from P-HS both at 30 degrees C and 42 deg
rees C but not from P-C. However, E sigma(70) transcribed rpoD not only fro
m P-C both at 30 degrees C and 42 degrees C but also from P-HS at 42 degree
s C. (C) 1999 Federation of European Microbiological Societies. Published b
y Elsevier Science B.V. All rights reserved.