FIG. 1.

Luciferase signal as reporter of SOS induction by mutant topoisomerase I cleavage complex. BW27784 transformed with luciferase reporter plasmid pDinlux along with either plasmid pAYOP (▵), plasmid pAYTOP128 (•), or plasmid pAYTOP-G122S (○) was grown to exponential phase in LB medium with ampicillin and chloramphenicol at 37°C until the A₆₀₀ reached 0.4. The culture was dispensed in 50-μl aliquots into white 96-well microtiter plates. Equal volume of LB medium containing 0.00001 to 0.004% arabinose was added for induction of recombinant Y. pestis topoisomerase I. The light production from the induced luciferase was measured on a Perkin-Elmer 7000 Plus BioAssay reader at 37°C in 10 min cycles with 30 s of shaking duration before each measurement. The luciferase response ratio was measured as the ratio of luciferase signal from the treated cultures versus the same culture that has not been treated with arabinose at 260 min after the addition of arabinose.