Elimination of lethal and pre-mutational DNA lesions during the photoreactivation of UV-irradiated Escherichia coli.

The comparison of the frequency of trp+ revertants of Escherichia coli B/r Hcr+ thy trp after UV-irradiation on the one hand and after UV-irradiation plus photoreactivation on the other showed that both photoreversible pyrimidine dimers of the cyclobutane type and the non-photoreversible DNA lesions cause, at equal lethal effects, also trp+ reversions with the same efficiency. If lethal, the pyrimidine dimers may thus be conceived as primary pre-mutational lesions.