Formation and excision of nitrofuran-DNA adducts in Escherichia coli.

When Escherichia coli were incubated with the strong mutagen 2[14C]2-amino-4-(5-nitro-2 furyl)-thiazole (ANFT) radioactivity became tightly and presumably covalently bound to DNA. Hydrolysis of the DNA with nucleases yielded low molecular weight radioactive material. The bound radioactivity was associated with at least two functionally and chemically distinct adducts. One of these was rapidly removed in uvr+ E. coli while the other was more persistent. Analysis of enzymatic hydrolysates on a Dowex AG 50W-X4 column showed that the 'excisable adducts' were chromatographically different from most of the persistent ones. ANFT caused daughter-strand gaps when the DNA of treated cells was replicated, provided this DNA contained excisable adducts. In situations where removal of these adducts was complete no gaps were found in newly synthesized DNA. 3-[14C]2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide (AF2) (another strongly mutagenic nitrofuran) became bound to the DNA of E. coli WP2 uvrA to a slightly greater extent than did [14C]ANFT. In contrast, [14C]nitrofurazone (the semicarbazide of 5-nitro-2-furaldehyde) a much weaker mutagen, gave considerably less binding. With AF2 and ANFT there was roughly the same relation between the amount of adduct formed and the subsequent yield of daughter strand gaps when the DNA replicated while with nitrofurazone the yield of gaps per adduct was somewhat lower. Incubation in vitro of [14C]ANFT with DNA in the presence of an E. coli nitrofuran reductase preparation also resulted in the binding of 14C to DNA.