Multiple loci affecting photoreactivation in Escherichia coli

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Abstract
Sutherland et al. mapped a phr gene in E. coli at 17 min and found that induction of an E. coli strain lysogenic for a .lambda. phage carrying this gene increased photoreactivating enzyme levels 2000-fold. Recently, Smith and Youngs and Sancar and Rupert located a phr gene at 15.9 min. The properties of photoreactivating enzyme and cellular photoreactivation in cells containing deletions of the gene at 17 min were investigated. Cells with this deletion photoreactivated UV-induced killing at a rate 20% of normal; they also contained approximately 20% of the normal photoreactivating enzyme level. The residual enzyme in these cells was characterized to determine whether the reduced cellular photoreactivation rate and photoreactivating enzyme levels resulted from reduced numbers of normal enzymes or from an altered enzyme. Photoreactivating enzymes from strains carrying a deletion of the region at 17 min had an apparent Km about 2- to 3-fold higher than normal enzyme and showed markedly increased heat lability. The gene at 17 min thus contains information determining the function of the E. coli photoreactivating enzyme rather than the quantity of the enzyme. The gene at 17 min is termed phrA and that located at 15.9 min is termed phrB.