The activity of sigma E, an Escherichia coli heat-inducible sigma-factor, is modulated by expression of outer membrane proteins.

Abstract

cr ~ and r ~2 are two heat-and ethanol-inducible g-factors in Escherichia coli. The cr 32 regulon is also induced by unfolded and misfolded proteins in the cytoplasm, and the function of many of the proteins in the cr 32 regulon is to bind to cytoplasmic proteins and assist them in folding or unfolding. To further understand the function of the cr F regulon, we searched for mutants that affected cr E activity. Our results indicate that a signal generated by expression of outer membrane proteins modulates cr E activity. Specifically, r ~ activity is induced by increased expression of OMPs and is reduced by decreased expression of OMPs. In addition, mutations that cause misfolded OMPs induce cr E activity. This signal is generated after the fate of OMPs and periplasmic proteins diverge in the secretory pathway and is not the result of an accumulation of OMP precursors in the cytoplasm. Our results indicate that this effect of OMPs is specific to the r E regnlon, because none of the above mutations affect r 32 activity. We propose that the ~r ~ regnlon is involved in processes that occur in extracytoplasmic compartments and that these two heat-inducible regulons may have distinct but complementary roles of monitoring the state of proteins in the cytoplasm (or 32) and outer membrane ((]rE).[Key Words: (r-Factors; protein export; outer membrane proteins; heat shock; (rE] Received September 13, 1993; revised version accepted October 14, 1993.In bacterial cells the (r-subunit directs RNA polymerase to initiate transcription at promoter sites on the DNA (Burgess et al. 1969). The primary (r-factor in the cell is responsible for transcription of most genes during exponential growth. In addition, alternative (r-factors direct transcription of sets of genes whose products are needed for specific functions, such as sporulation, nitrogen fixation, or flagella synthesis {Gross et al. 1992). Alternative (r-factors are often activated by changes in environmental or cellular conditions that generate morphological and/or molecular cues, signaling the need for the gene products in the regulon under control of a particular (r-factor. Elucidation of these signal-transduction pathways provides insights about global control of gene activity in prokaryotic cells.The activity of two Escherichia coli alternative (r-factors, (r32 and (re ((r24), increases after temperature upshift or exposure to ethanol {Grossman et al. 1984;Erickson et al. 1987;Straus et al. 1987;Erickson and Gross 1989;Wang and Kaguni 1989}. RNA polymerase (E) containing o ~2 (E(r 32) transcribes the heat shock genes with products that consist primarily of chaperones and proteases.

Heat shock induction by a misassembled cytoplasmic membrane protein complex in Escherichia coli

“…As we have shown that the L3 loop of MalF is responsible for the stress induction, it is possible that this loop indirectly activates the 24 -dependent pathway from the periplasm by interfering with the membrane insertion of some outer membrane proteins or with the localization and folding of some periplasmic proteins. However, it has been shown that a reduction in the efficiency of translocation is more likely to provoke a reduction in the level of phtrA induction (Mecsas et al, 1993).…”

Amplification of a novel gene, sanA, abolishes a vancomycin-sensitive defect in Escherichia coli

“…First, because there is no apparent transcription promoter inside cdd or between cdd and sanA, a possible cotranscription of these two genes from the CytR-and cAMP receptor protein-cAMPregulated cdd promoter (18) must be envisaged. Second, some of the small number of genes already mapped in this chromosomal region appear to be involved in outer membrane function or assembly: (i) an extragenic suppressor (sfaA) of ompF assembly mutants (34) and of LPS mutants defective in porin assembly (25), (ii) a gene (phmD) coding for a cell envelope component whose expression increases as a function of the external pH (16), (iii) a locus (ise-48) that increases E ( 24 ) factor activity when present in multicopies (32), (iv) a gene conferring bicyclomycin resistance (2), and (v) a gene (pmrD) from S. typhimurium that confers resistance to the outer membrane-damaging drug polymyxin B when expressed from a medium-copy-number plasmid (46). It remains to be seen if one of these loci and sanA have something in common.…”

“…This indicated either a deletion or the insertion of an element of several kilobases in the chromosomal sanA region of this strain. To distinguish between these two possibilities, the PCR-amplified 0.9-kb fragment was extracted from an agarose gel, 32 P labelled, and used as a probe to hybridize with chromosomal DNAs of strains K802 and 87.6 digested with six different restriction enzymes. Again hybridization was observed with the fragmented K802 DNA but was totally absent in the case of the fragmented DNA from 87.6 (data not shown).…”

The Escherichia coli phage‐shock‐protein (psp) operon

“…Other than expression of gene IV or infection with filamentous phage, all the inducing stimuli also induce the 32 -dependent heat-shock genes (groE, dnaK, dnaJ, grpE (Lindquist and Craig, 1988;Yura et al, 1993)), but psp-operon transcription does not require 32 and hence none of the other components of the canonical heat-shock response; indeed, shift of a 32ts mutant to the non-permissive temperature intensifies the psp response, and for the stimuli that induce psp transiently, such as heat and exposure to ethanol, this prolongs the response (Brissette et al, 1990;Weiner et al, 1991). A participant in the canonical heatshock response of E. coli is E , which is responsible for transcription of 32 at 50ЊC (Erickson and Gross, 1989) and is itself activated by overproduction of outer membrane proteins (Mecsas et al, 1993). Sigma E is not required for psp-operon induction, and expression of pIV does not activate E or induce its synthesis (our unpublished results).…”