Heat shock regulation in the ftsH null mutant of Escherichia coli: dissection of stability and activity control mechanisms of sigma32 in vivo.
The heat shock response of Escherichia coli is regulated by the cellular level and the activity of sigma32, an alternative sigma factor for heat shock promoters. FtsH, a membrane-bound AAA-type metalloprotease, degrades sigma32 and has a central role in the control of the sigma32 level. The ftsH null mutant was isolated, and establishment of the DeltaftsH mutant allowed us to investigate control mechanisms of the stability and the activity of sigma32 separately in vivo. Loss of the FtsH function caused marked stabilization and consequent accumulation of sigma32 ( approximately 20-fold of the wild type), leading to the impaired downregulation of the level of sigma32. Surprisingly, however, DeltaftsH cells express heat shock proteins only two- to threefold higher than wild-type cells, and they also show almost normal heat shock response upon temperature upshift. These results indicate the presence of a control mechanism that downregulates the activity of sigma32 when it is accumulated. Overproduction of DnaK/J reduces the activity of sigma32 in DeltaftsH cells without any detectable changes in the level of sigma32, indicating that the DnaK chaperone system is responsible for the activity control of sigma32 in vivo. In addition, CbpA, an analogue of DnaJ, was demonstrated to have overlapping functions with DnaJ in both the activity and the stability control of sigma32.
Tatsuta
T
T
Department of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kumamoto 862-0976, Japan.
Tomoyasu
T
T
Bukau
B
B
Kitagawa
M
M
Mori
H
H
Karata
K
K
Ogura
T
T
D049069:ATP-Dependent Proteases; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018834:Chaperonin 60 / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018869:Heat-Shock Response / Q000235:genetics*; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics*; D012808:Sigma Factor / Q000378:metabolism*; D013696:Temperature
D001426:Bacterial Proteins; C085674:CbpA protein, E coli; D018834:Chaperonin 60; D004268:DNA-Binding Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D012808:Sigma Factor; D007544:Isopropyl Thiogalactoside; D049069:ATP-Dependent Proteases; C513383:FtsH protein, E coli; C063842:dnaK protein, E coli