Figure 3.

uvrD mutants are resistant to 8-methoxypsoralen despite an inability to incise interstrand cross-links. (A) Cultures containing the plasmid pBR322 were UVA irradiated with 5.7 kJ/m² in the presence of 20-μg/ml 8-methoxypsoarlen and then allowed to recover. To observe the cross-links remaining in the DNA at each time point, total genomic and plasmid DNA was purified from cells, restricted with HindIII to linearize the plasmid, and examined by Southern analysis following alkali gel electrophoresis using ³²P-labeled pBR322 as a probe. Lane U, untreated cells. (B) The fraction of cross-links remaining in the DNA during the recovery period is plotted for wild type (WT) (▪), uvrA (●), and uvrD (○). The initial percentage of cross-linked plasmids immediately following UVA irradiation were 3.6 ± 1.0% for wild type, 7.9 ± 2.3% for uvrA, and 6.6 ± 0.7% for uvrD. Plots represent the average of seven experiments for wild type and four experiments for uvrA and uvrD. Error bars represent SEM.