Co-operative Study on the Mechanisms of DNA Damage Induced by Vacuum-UV above 50 nm.

The results of this study are as follows : (1) A new phenomenon was discovered for photoacoustic measurements of molecular gases. The amplitude signals measured by the microphone method exhibited minima, instead of maxima, corresponding to the absorption maxima in the vacuum-UV (VUV) region. (2) The spin-trapping method was applied to measure radicals of nucleotides in solids induced by 160 nm photons, but failed due to insufficient intensity. (3) The main photoproducts of sublimed thymine films were determined by the HPLC method : cyclobutane-type dimers and (6-4) photoproducts above 150 nm and below 140 nm 5-hydroxymethyluracil and 5-formyluracil. (4) The action spectra for forming the cyclobutane-type dimer and (6-4) photoproduct in dry DNA were determined at between 150 and 300 nm by specific monoclonal antibodies. (5) Double-strand breaks (dsb) in DNA in solution were measured at 160 and 180 nm, indicating that dsb was induced more efficiently by 160 nm photons than 180 nm photons. (6) A new simple method which can be used to determine the base sequence of mutant DNA of Bacillus subtilis was developed. The preliminary results indicate that certain types of rare mutations were selectively induced by UV and soft X-rays under high vacuum. (7) The action spectrum for the inactivation of lysozyme and degradation pattern of amino acids was determined above 60 nm.