RPOE, THE GENE ENCODING THE 2ND HEAT-SHOCK SIGMA-FACTOR, SIGMA(E), INESCHERICHIA-COLI

In Escherichia coli, the heat shock response is under the control of t wo alternative sigma factors: sigma(32) and sigma(E). The sigma(32)-re gulated response is well understood, whereas little is known about tha t of sigma(E), except that it responds to extracytoplasmic immature ou ter membrane proteins. To further understand this response, we located the rpoE gene at 55.5' and analyzed the role of sigma(E). sigma(E) is required at high temperature, and controls the transcription of at le ast 10 genes. Some of these might contribute to the integrity of the c ell since Delta poE cells are more sensitive to SDS plus EDTA and crys tal violet. sigma(E) controls its own transcription from a sigma(E)-de pendent promoter, indicating that rpoE transcription plays a role in t he regulation of E sigma(E) activity. Indeed, under steady-state condi tions, the transcription from this promoter mirrors the levels of E si gma(E) activity in the cell. However, it is unlikely that the rapid in crease in E sigma(E) activity following induction can be accounted for solely by increased transcription of rpoE. Based upon homology argume nts, we suggest that a gene encoding a negative regulator of sigma(E) activity is located immediately downstream of rpoE and mag function as the target of the E sigma(E) inducing signal.