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Heat shock regulation in the ftsH null mutant of Escherichia coli : dissection of stability and activity control mechanisms of σ 32 in vivo
Author(s) -
Tatsuta Takashi,
Tomoyasu Toshifumi,
Bukau Bernd,
Kitagawa Masanari,
Mori Hirotada,
Karata Kiyonobu,
Ogura Teru
Publication year - 1998
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1998.01091.x
Subject(s) - biology , mutant , heat shock protein , escherichia coli , heat shock , in vivo , microbiology and biotechnology , chaperone (clinical) , wild type , overproduction , biochemistry , gene , genetics , medicine , pathology
The heat shock response of Escherichia coli is regulated by the cellular level and the activity of σ 32 , an alternative sigma factor for heat shock promoters. FtsH, a membrane‐bound AAA‐type metalloprotease, degrades σ 32 and has a central role in the control of the σ 32 level. The ftsH null mutant was isolated, and establishment of the Δ ftsH mutant allowed us to investigate control mechanisms of the stability and the activity of σ 32 separately in vivo . Loss of the FtsH function caused marked stabilization and consequent accumulation of σ 32 (≈20‐fold of the wild type), leading to the impaired downregulation of the level of σ 32 . Surprisingly, however, Δ ftsH 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 σ 32 when it is accumulated. Overproduction of DnaK/J reduces the activity of σ 32 in Δ ftsH cells without any detectable changes in the level of σ 32 , indicating that the DnaK chaperone system is responsible for the activity control of σ 32 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 σ 32 .