Dynamic interplay between antagonistic pathways controlling the sigma 32 level in Escherichia coli.
The heat-shock response in Escherichia coli depends primarily on the transient increase in the cellular level of heat-shock sigma factor final sigma(32) encoded by the rpoH gene, which results from both enhanced synthesis and transient stabilization of normally unstable final sigma(32). Heat-induced synthesis of final sigma(32) was previously shown to occur at the translation level by melting the mRNA secondary structure formed within the 5' coding sequence of rpoH including the translation initiation region. The subsequent decrease in the final sigma(32) level during the adaptation phase has been thought to involve both shutoff of synthesis (translation) and destabilization of final sigma(32)-mediated by the DnaK-DnaJ chaperones, although direct evidence for translational repression was lacking. We now show that the heat-induced synthesis of final sigma(32) does not shut off at the translation level by using a reporter system involving translational coupling. Furthermore, the apparent shutoff was not observed when the synthesis rate was determined by a very short pulse labeling (15 s). Examination of final sigma(32) stability at 10 min after shift from 30 to 42 degrees C revealed more extreme instability (t(1/2)=20 s) than had previously been thought. Thus, the dynamic change in final sigma(32) stability during the heat-shock response largely accounts for the apparent shutoff of final sigma(32) synthesis observed with a longer pulse. These results suggest a mechanism for maintaining the intricate balance between the antagonistic pathways: the rpoH translation as determined primarily by ambient temperature and the turnover of final sigma(32) as modulated by the chaperone (and presumably protease)-mediated autogenous control.
Morita
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MT
HSP Research Institute, Kyoto Research Park, Shimogyo-ku, Kyoto 600-8813, Japan.
Kanemori
M
M
Yanagi
H
H
Yura
T
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology; D006360:Heat-Shock Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D006358:Hot Temperature; D018832:Molecular Chaperones / Q000502:physiology; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012808:Sigma Factor; D014157:Transcription Factors / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
D001426:Bacterial Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; C063842:dnaK protein, E coli