Regulation of breakdown of canavanyl proteins in Escherichia coli by growth conditions in Ion+ and Ion− cells

In vivo rates of proteolysis of canavanyl proteins were compared in lon+ and lon- Escherichia coli strains following growth in a variety of media. Both lon+ and lon- cells grown rapidly in complex media possessed higher levels of constitutive degradative activity than when cultured in minimal media. Pre-growth of lon+ cells in the presence of canavanine induced proteolytic activity following growth in minimal media as did stress agents such as heat, alcohol and puromycin: the lon mutant did not show the increased activity following canavanine treatment. The results suggest the presence of a proteolytic activity which selectively degrades aberrant proteins which does not involve protease La, the product of the lon gene, and which furthermore is regulated in part by growth conditions independently of the stress response.