Ultraviolet-stimulated DNA synthesis in toluenzied Escherichia coli deficient in DNA polymerase I.

Ultraviolet (UV)-stimulated nonconservative DNA synthesis has been observed in E. coli rendered permeable to nucleoside triphosphates by exposure to toluene. This synthesis is detected in toluenized cells in which the background of UV-independent DNA synthesis is reduced by use of dnaB mutants temperature-sensitive for DNA replication and additionally deficient in DNA polymerase I. UV-stimulated nonconservative synthesis is also seen in polA dnaE mutants that are deficient in two of the three known DNA polymerases. The observed UV-stimulated repair-like synthesis requires the presence of the four deoxyribonucleoside triphosphates and ATP. This mode of synthesis appears to differ from the ATP-independent nonconservative DNA synthesis previously reported to occur in toluenized bacteria.