Abstract
A multicopy clone was isolated which conferred resistance to the SOS inducer nitrofurantoin in an Escherichia coli lon mutant. Plasmid pHL1 was found to contain a 7–8 kbp HindIII DNA insert from a region of the chromosome at 88.5 minutes. Further characterisation of pHL1 revealed that resistance to nitrofurantoin was due to the overexpression of the hslV-hslU operon which encodes an ATP-dependent protease complex in E. coli. The overexpression of hslVU also conferred resistance to ultraviolet irradiation in the lon mutant. It is proposed that when overproduced, the HslV-HslU protease complex can degrade SulA which is an endogenous inhibitor of the essential cell division protein FtsZ. The ability of HslVU to degrade SulA in vivo suggests that Lon and HslVU may share a range of substrates. Furthermore, the suppression of lon could be used as a simple genetic test of proteolytic activity of cloned HslVU.
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