Abstract
In this work, an over-expressed cyclobutane pyrimidine dimer (CPD) photolyase of Synechococcus sp. PCC 7942 was used to investigate UV-C (ultraviolet irradiation of C-region) influence on photoreactivation. In vivo photoreactivation experiments indicated that the survival rate decreased from 100 to 2.6% when the UV-C flux was increased from 1.1 to 68.5 muW/cm2. It seemed that the photolyase was easily inactivated at UV-C intensities >or=25.5 muW/cm2. Spectrometric analysis indicated that tertiary structure of the photolyase changed evidently when the UV-C fluxes were >or=25.5 muW/cm2, while the secondary structure was almost unchanged even at 170 muW/cm2. Band shift assay indicated that catalytic activity of the photolyase was impaired at fluxes >or=25.5 muW/cm2, but no significant influence on DNA-binding activity was observed. These results suggest that photoreactivation is efficient at UV-C fluxes <or=25.5 muW/cm2, but would be impaired by intense UV-C irradiation due to structure changes of the photolyase.
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