[Plasmid DNA strand breaks induced by laser irradiation of 193 nm wavelength].
DNA of plasmid pBR322 irradiated with laser at a wavelength of 193 mm was treated with an extract containing proteins from E.coli K12 AB1157 (wild-type). The enzymes were found to produce single- and double-strand DNA breaks, which was interpreted as a transformation of a portion of cyclobutane pyrimidine dimers and (6-4) photoproducts into nonrepairable single-strand DNA breaks. The products resulted from ionization of DNA, in particular, single-strand breaks, transform to double-strand breaks. A comparison of these data with the data on survival of plasmid upon transformation of E.coli K12 AB1157 enables one to assess the biological significance of single- and double-strand breaks. The inactivation of the plasmid (in AB1157) is mainly determined by the number of directly formed laser-induced single-strand breaks, whereas the contribution of enzymatically produced single- and double-strand breaks is insignificant.
Gurzadian
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GG
Max-Planck Institute of Radiation Chemistry, Mühlheim-on-Ruhr, Germany.
Schulte-Frohlinde
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D004249:DNA Damage; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D007834:Lasers; D010957:Plasmids / Q000235:genetics*
D004269:DNA, Bacterial