HEAT-SHOCK REGULATION IN THE FTSH NULL MUTANT OF ESCHERICHIA-COLI - DISSECTION OF STABILITY AND ACTIVITY CONTROL MECHANISMS OF SIGMA(32) IN-VIVO

The heat shock response of Escherichia coli is regulated by the cellul ar level and the activity of sigma(32), a, alternative sigma factor fo r heat shock promoters. FtsH, a membrane-bound AAA-type metalloproteas e, degrades sigma(32) and has a central role in the control of the sig ma(32) level. The ftsH null mutant was isolated, and establishment of the Delta ftsH mutant allowed us to investigate control mechanisms of the stability and the activity of sigma(32) separately in vivo. Loss o f the FtsH function caused marked stabilization and consequent accumul ation of sigma(32) (approximate to 20-fold Of the wild type), leading to the impaired downregulation of the level of sigma(32). Surprisingly , however, Delta ftsH cells express heat shock proteins only two- to t hreefold 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 sigma(32) when it is accumulated. Overproduction of DnaK/J reduces th e activity of sigma(32) in Delta ftsH cells without any detectable cha nges in the level of sigma(32), indicating that the DnaK chaperone sys tem is responsible for the activity control of sigma(32) in vivo. In a ddition, CbpA, an analogue of DnaJ, was demonstrated to have overlappi ng functions with DnaJ in both the activity and the stability control of sigma(32).