INDUCTION OF LAMBDA-PROPHAGE BY 213 NM LASER-RADIATION - A QUANTITATIVE COMPARISON WITH 193 NM EXCIMER RADIATION USING IMAGE-ANALYSIS

We compared the DNA damage produced by radiation from two UV laser wav elengths, 213 nm and 193 nm, with that produced by noncoherent 254 nm radiation, Following irradiation of Escherichia coli BR339, a bacterio phage lambda lysogen containing the lacZ gene, prophage induction was measured by assaying for beta-galactosidase, Because of the limited pe netration by UV laser wavelengths an agar overlay of the lysogen was u sed as the irradiation target, Irradiation of 254 nm was performed in buffer suspension followed by transfer of 5 mu L spots onto assay plan ts, Computer image analysis was used to monitor the rate of product fo rmation, observed as an increase in optical density of the irradiated zones on assay plates, We found that the rate of product formation was a more reproducible unit of comparison than the optical density prese nt at the end of the reaction. Although the rate of product formation was not linearly related to enzyme concentration, the data could be fi t to a simple logarithmic function, Using this method, we concluded th at the DNA damaging ability of 213 nm radiation was 10 times more effi cient than 193 nm radiation and about 100 times less efficient than 25 4 nm noncoherent radiation.