Influence of Ultraviolet-C on Structure and Function of Synechococcus sp. PCC 7942 Photolyase

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L. W. Zhang, M. Li, and Q. Y. Wu^*

Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, P. R. China; fax: 86-10-627-81825; E-mail: qingyu@tsinghua.edu.cn

^* To whom correspondence should be addressed.

Received September 22, 2006; Revision received February 12, 2007

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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 µW/cm². It seemed that the photolyase was easily inactivated at UV-C intensities ≥25.5 µW/cm². Spectrometric analysis indicated that tertiary structure of the photolyase changed evidently when the UV-C fluxes were ≥25.5 µW/cm², while the secondary structure was almost unchanged even at 170 µW/cm². Band shift assay indicated that catalytic activity of the photolyase was impaired at fluxes ≥25.5 µW/cm², but no significant influence on DNA-binding activity was observed. These results suggest that photoreactivation is efficient at UV-C fluxes ≤25.5 µW/cm², but would be impaired by intense UV-C irradiation due to structure changes of the photolyase.

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KEY WORDS: circular dichroism (CD) spectrum, cyclobutane pyrimidine dimer (CPD) photolyase, fluorescence spectrum, Synechococcus sp. PCC 7942, ultraviolet resistance

DOI: 10.1134/S0006297907050100

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