A novel sigma factor is involved in expression of the rpoH gene of Escherichia coli

Abstract

The Escherichia coli rpoH gene encoding J32, which is involved in the heat shock response, is transcribed from as many as four promoters. We have isolated a novel sigma factor of about 24 kilodaltons that allows core RNA polymerase to transcribe preferentially from one of these promoters, rpoH3p. This promoter is known to be regulated by DnaA protein. The,24 factor was isolated from a preparation of RNA polymerase by electroelution from sodium dodecyl sulfate-polyacrylamide gels followed by renaturation. Expression of heat shock proteins is induced by treatments which include those that induce the stringent response. Under such conditions, decreased transcription from rpoH3p and no increase in transcription from other rpoH promoters were observed. This result suggests that induction of heat shock proteins by the stringent response is not mediated by increased transcription of the rpoH gene. (8,14,21). Upon temperature upshift, the increased expression of heat shock proteins is attributable to an increase in u32 due to increased expression and stability (10,11,31,32). A reprogramming of RNA polymerase ensues.Receht experiments have examined transcription of the rpoH gene (10,11,32). Four promoters, designated rpoHip, rpoH2p, rpoH3p, and rpoH4p, have been mapped at about 220, 130, 90, and 80 base pairs, respectively, upstream from the coding sequence (10, 11). Promoters rpoHlp and rpoH4p are recognized by U70 RNA polymerase (Eu70) (3, 10, 11). A third promoter, rpoH2p, appears to be strain specific. In vitro transcription from the fourth promoter, rpoH3p, does not involve Eu70 or Eu32 (3, 10). These results suggest that a novel sigma factor or a positive regulatory protein may be required for transcription from rpoH3p. In related experiments examining regulation of the rpoH gene, we identified a preparation of RNA polymerase able to initiate transcription from rpoHip, rpoH3p, and rpoH4p (33a). From this, we have isolated a protein of 24 kilodaltons (kDa) which confers rpoH3p-specific transcription to core RNA polymerase. We also report on transcriptional regulation of the rpoH gene during the stringent response. MATERIALS AND METHODSBacterial strains and plasmids. E. coli W3110 and AB1157 thr-J ara-14 leuB6 (gpt-proA)62 lacYl tsx-33 supE44 galK2 hisG4 rpsL31 xyl-5 mtl-l argE3 thi-J were from the E. coli Genetic Stock Center. Plasmid pFN82 was from Frederick C. Neidhardt (University of Michigan). To construct this plasmid, a 2.5-kilobase-pair PstI fragment containing the rpoH promoter region and adjacent N-terminal coding region was inserted at the single PstI site of pBR322 (27)

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“…2), show striking similarity to the cE (a24) promoters. u2 is a 24-kDa sigma factor (19,56,78) involved in expression of J32, the heat shock sigma factor in E.…”

Identification of the Escherichia coli sohB gene, a multicopy suppressor of the HtrA (DegP) null phenotype

“…The transcription of members of this regulon is positively regulated by a new a factor, known as (24 (CE) (4,39). So far, the only two genes which are known to be transcribed by a24 are rpoH and htrA (degP) (4,5,20,39).…”

The rpoE gene of Escherichia coli, which encodes sigma E, is essential for bacterial growth at high temperature

“…The primary factor, 70 encoded by rpoD, is responsible for transcription of the majority of the genes expressed during exponential growth. In addition, alternative factors direct transcription of sets of genes whose products are needed for specific functions, such as nitrogen fixation, flagellum synthesis, heat shock response, and stationary-phase growth (4).The activities of two alternative factors, 32 and E , increase after the cell is exposed to a high temperature or ethanol (2,3,5,21,25,28). RNA polymerase containing 32 (E 32 ) transcribes the heat shock genes whose products are related to chaperones and proteases (29).…”

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