RECOGNITION OF MITOMYCIN-C DNA MONOADDUCTS BY UVRABC NUCLEASE

The Escherichia coli UVRABC nuclease assay has been shown to be an excellent method to monitor mitomycin C-DNA monoalkylation transformations. Analysis of the mitomycin C-induced and 10-decarbamoylmitomycin C-induced DNA incision sites from rive different DNA restriction fragments after UVRABC treatment revealed that all the drug-induced UVRABC incisions can be attributed to drug bonding at guanine residues and that bonding proceeded in a highly sequence selective manner. The densitometric data indicated that both the 5' and 3' nearest neighbor bases surrounding the guanine site affect its susceptibility to drug modification. Mitomycin lesions occurred predominantly at 5'CG sequences, and 5'CGG sequences were the preferred trinucleotide units for mitomycin C monoalkylation transformations. Potential contributing factors (i.e., C(10) carbamate moiety, C(8) hydroquinone hydroxyl group) responsible for the sequence selectivity of this process have been examined and a rationale offered for the DNA bonding specificity. The advantages of the UVRABC assay versus the previously employed lambda-exo protocol for the detection of mitomycin C monoalkylation sites are discussed.