Photolesions and biological inactivation of plasmid DNA on 254 nm irradiation and comparison with 193 nm laser irradiation.

Plasmid pTZ18R and calf thymus DNA in aerated neutral aqueous solution were irradiated by continuous 254 nm light. The quantum yields are phi ssb = 4.0 x 10(-5) and phi dsb = 1.4 x 10(-6) for single- and double-strand break formation, respectively, phi br = 2.3 x 10(-5) for base release, phi dn = 2.1 x 10(-3) for destruction of nucleotides, and phi icl approximately phi lds approximately 1 x 10(-6) for interstrand cross-links and locally denatured sites, respectively. The presence of Tris-HCl/ethylenediaminetetraacetic acid (10:1, pH 7.5) buffer strongly reduces phi ssb. The corresponding phi values, obtained on employing pulsed 193 nm laser irradiation, are much larger than those using lambda 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 (lambda irr = 254 nm) were measured by transformation of the Escherichia coli strains AB1157 (wild type), phi ina (1157) = 1.6 x 10(-4), AB1886 (uvr-), phi ina (1886) = 4.2 x 10(-4), AB2463 (rec-), phi ina (2463) = 4.1 x 10(-4) and AB2480 (uvr- rec-), phi ina (2480) = 3.1 x 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.(ABSTRACT TRUNCATED AT 250 WORDS)