SOS response of RecA variant proteins.

<p>RecA variant strains containing a plasmid expressing GFP under SOS control (utilizing the <i>recN</i> promoter) were grown in LB. Specific fluorescence, defined as measured fluorescence divided by the OD₆₀₀, is shown. (A) The SOS response in cells expressing RecA variant proteins without treatment with any DNA damaging agent. (B) The SOS response in cells expressing RecA variant proteins after induction by adding 0.005 μg/ml ciprofloxacin at 180 minutes. Due to the error inherent in dividing very small numbers, specific fluorescence is not displayed for times prior to 200 and 230 min in panels A and B, respectively.