Increased ATP-dependent proteolytic activity in lon-deficient Escherichia coli strains lacking the DnaK protein.

Extracts made from Escherichia coli null dnaK strains contained elevated levels of ATP-dependent proteolytic activity compared with levels in extracts made from dnaK+ strains. This ATP-dependent proteolytic activity was not due to Lon, Clp, or Alp-associated protease. Comparison of the levels of ATP-dependent proteolytic activity present in lon rpoH dnaK mutants and in lon rpoH dnaK+ mutants showed that the level of ATP-dependent proteolytic activity was elevated in the lon rpoH dnaK mutant strain. These findings suggest that DnaK negatively regulates a new ATP-dependent proteolytic activity, independently of sigma 32. Other results indicate that an ATP-dependent proteolytic activity was increased in a lon alp strain after heat shock. It is not yet known whether the same protease is associated with the increased ATP-dependent proteolytic activity in the dnaK mutants and in the heat-shocked lon alph strain.