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J. Bacteriol., Sep 1995, 5222-5231, Vol 177, No. 18
J Xu and RC Johnson
Fis is a general nucleoid-associated protein in Escherichia coli whose
expression is highly regulated with respect to growth conditions. A random
collection of transposon-induced lac fusions was screened for those which
give increased expression in the presence of Fis in order to isolate a
ProP-LacZ protein fusion. We find that proP, which encodes a low-affinity
transporter of the important osmoprotectants proline and glycine betaine,
is transcribed from two promoters. proP1 is transiently induced upon
subculture and is upregulated by increases in medium osmolarity. As cells
enter stationary phase, a second promoter, proP2, is strongly induced. This
promoter can also be induced by high medium osmolarity in exponential
phase. The activity of proP2 depends on Fis and the stationary-phase sigma
factor sigmas. In the presence of Fis, proP2 expression is increased over
50-fold, as judged by the LacZ activity of cells carrying the proP-lacZ
fusion as well as by direct RNA analysis, making this the most strongly
activated promoter by Fis that has been described. Two Fis binding sites
centered at positions - 41 (site I) and -81 (site II) with respect to the
transcription initiation site of P2 have been defined by DNase I
footprinting. Mutations in site I largely abolish stationary-phase
activation, while mutations at site II have a minor effect, suggesting that
direct binding of Fis to site I is important for Fis-mediated activation of
this promoter. In addition to Fis and sigmas, sequences located over 108 bp
upstream of the proP2 transcription initiation site are required for
efficient expression.
Copyright © 1995, American Society for Microbiology
Fis activates the RpoS-dependent stationary-phase expression of proP in Escherichia coli
Department of Biological Chemistry, UCLA School of Medicine 90095, USA.
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