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PHOTOLESIONS AND BIOLOGICAL INACTIVATION OF PLASMID DNA ON 254 nm IRRADIATION AND COMPARISON WITH 193 nm LASER IRRADIATION
Author(s) -
Gurzadyan Gagik G.,
Gorner Helmut,
SchulteFrohlinde Dietrich
Publication year - 1993
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1993.tb04918.x
Subject(s) - plasmid , escherichia coli , dna , pyrimidine dimer , irradiation , chemistry , microbiology and biotechnology , strain (injury) , biology , dna damage , biochemistry , physics , gene , anatomy , nuclear physics
Plasmid pTZ18R and calf thymus DNA in aerated neutral aqueous solution were irradiated by continuous 254 nm light. The quantum yields are φ ssb = 4.0 × 10 ‐5 and φ dsb = 1.4 × 10 ‐6 for single‐ and double‐strand break formation, respectively, φ br = 2.3 × 10 ‐5 for base release, φ dn = 2.1 × 10 ‐3 for destruction of nucleotides, and φ icl ×φ lds × 1 × 10 ‐6 for interstrand cross‐links and locally denatured sites, respectively. The presence of Tris‐HCI/ ethylenediaminetetraacetic acid (10:1, pH 7.5) buffer strongly reduces φ ssb , The corresponding φ values, obtained on employing pulsed 193 nm laser irradiation, are much larger than those using λ irr , = 254 nm. This is ascribed to a contribution of chemical reactions induced by photoionization, which is absent for 254 nm irradiation. The quantum yields of inactivation of plasmid DNA (λ irr = 254 nm) were measured by transformation of the Escherichia coli strains AB1157 (wild type), φ ina (1157) = 1.6 × 10 ‐4 , AB1886 (uvr ‐ ), φ ina (1886) = 4.2 × 10 ‐4 , AB2463 (rec ‐ ), φ ina (2463) = 4.1 × 10 ‐4 and AB2480 (uvr ‐ rec ‐ ), φ ina (2480) = 3.1 × 10 ‐3 . The quantum yields of inactivation of plasmid DNA are compared with those of the four E. coli strains (denoted as chromosomal DNA inactivation) obtained from the literature. The results for E. coli strain AB2480 show that the chromosomal DNA and the plasmid DNA are both inactivated by a single pyrimidine photodimer per genome. With the E. coli strain AB2463 inactivation of plasmid and chromosomal DNA is the same for the same total damage per genome and is ∼ 10 times smaller than for AB2480. This is explained by photodimer repair in chromosomal and plasmid DNA and by the absence of dsb repair in both cases. In the repair wild‐type strain AB1157, inactivation of the plasmid DNA is roughly 100 times higher than that of the chromosomal DNA. We postulate that a portion of this difference is due to repair of dsb by the recA system in chromosomal DNA and that such repair does not take place in the plasmid DNA. The biological results from 254 nm irradiation are compared with those from 193 nm laser irradiation.