Pn. Danese et al., ACCUMULATION OF THE ENTEROBACTERIAL COMMON ANTIGEN LIPID-II BIOSYNTHETIC INTERMEDIATE STIMULATES DEGP TRANSCRIPTION IN ESCHERICHIA-COLI, Journal of bacteriology (Print), 180(22), 1998, pp. 5875-5884
In Escherichia coli, transcription of the degP locus, which encodes a
heat-shock-inducible periplasmic protease, is controlled by two parall
el signal transduction systems that each monitor extracytoplasmic prot
ein physiology. For example, the heat-shock-inducible sigma factor, si
gma(E), controls degP transcription in response to the overproduction
and folded state of various extracytoplasmic proteins. Similarly, the
CpxA/R two-component signal transduction system increases degP transcr
iption in response to the overproduction of a variety of extracytoplas
mic proteins. Since degP transcription is attuned to the physiology of
extracytoplasmic proteins, we were interested in identifying negative
transcriptional regulators of degP. To this end, we screened for null
mutations that increased transcription from a strain containing a deg
P-lacZ reporter fusion. Through this approach, we identified null muta
tions in the wecE, rmlA(ECA), and wecF loci that increase degP transcr
iption. Interestingly, each of these loci is responsible for synthesis
of the enterobacterial common antigen (ECA), a glycolipid situated on
the outer leaflet of the outer membrane of members of the family Ente
robacteriaceae. However, these null mutations do not stimulate degP tr
anscription by eliminating ECA biosynthesis. Rather, the wecE, rmlA(EC
A), and wecF null mutations each impede the same step in ECA biasynthe
sis, and it is the accumulation of the ECA biosynthetic intermediate,
lipid II, that causes the observed perturbations. For example, the lip
id II-accumulating mutant strains each (i) confer upon E. coli a sensi
tivity to bile salts, (ii) confer a sensitivity to the synthesis of th
e outer membrane protein LamB, and (iii) stimulate both the Cpx pathwa
y and sigma(E) activity. These phenotypes suggest that the accumulatio
n of lipid II perturbs the structure of the bacterial outer membrane.
Furthermore, these results underscore the notion that although the Cpx
and sigma(E) systems function in parallel to regulate degP transcript
ion, they can be simultaneously activated by the same perturbation.