UV irradiation assay. A) M. smegmatis wild type, S1 (uvrA::tn611), S1-uvrA-Ms and S1-uvrA-Tb strains were streaked from left to right on LB plates. Plates were either exposed or not to UV radiation (0, 15, 30 and 45 seconds). B) M. smegmatis wild type, S1, S1-uvrA-Ms and S1- uvrA-Tb cells in exponential phase were harvested and resuspended in PBS (see Methods for details). Aliquots were exposed to different UV doses (0, 2, 4 and 6 mJ/cm2). The percentage of survival of each strain was determined and represented as the mean value of three independent experiments.