US EPA

1069595 

Journal Article 

Mutation induction and killing of Escherichia coli by DNA adducts and crosslinks: A photobiological study with 8-methoxypsoralen 

Bridges, BA; Mottershead, RP; Knowles, A 

1979 

Yes 

Chemico-Biological Interactions
ISSN: 0009-2797
EISSN: 1872-7786 

27 

2-3 

221-233 

English 

387266 

10.1016/0009-2797(79)90127-3 

WOS:A1979HU40600007 

Low doses of 350 nm radiation (NUV) in the presence of 8-methoxypsoralen (8-MOP) induce predominantly mono-adducts in bacterial DNA. Further exposure to NUV in the absence of 8-MOP converts a proportion of these mono-adducts to interstrand cross-links. Using this approach the relative effects of adducts and cross-links on bacteria with different repair capacities was studied. Escherichia coli WP100 uvrA recA, believed to be totally deficient in the ability to repair 8-MOP plus NUV damage to DNA, was inactivated on average by a single photon event occurring with a quantum efficiency of about 0.03. We conclude that the inactivating lesion is probably a single mono-adduct. E. coli WP2 uvrA, deficient in excision endonuclease activity, may be inactivated by a very small number of cross-links, probably one. These conclusions are consistent with present knowledge of the repair capabilities of these bacteria. Conversion of mono-adducts to cross-links in WP2 uvrA (which occurs with a quantum efficiency of around 0.3) greatly increases lethality but results in a reduction of the induced mutation frequency presumably because cross-links are (almost) invariably lethal. In the repair-proficient strain WP2 both adducts and cross-links can be repaired but the latter are more likely than the former to lead to either death or mutation.