期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1975
卷号：72
期号：1
页码：167-171
DOI：10.1073/pnas.72.1.167
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：A method was developed in which E. coli cells were irradiated with four MeV electrons and transferred to alkaline detergent within a fraction of a second. This technique minimizes the amount of repair of radiation damage before analysis without the necessity of using physical or chemical treatments to inhibit repair and alter the physiological condition of the cells. The yield of DNA strans breaks formed in covalent circular superhelical lambda DNA molecules superinfecting E. coli lysogens was about 4-fold greater when the cells were irradiated in oxygen than when they were irradiated under nitrogen anoxia. The same yields were obtained in phosphate buffer at 3 degrees and 22 degrees as well as in growth medium at 37 degrees, and the yields were not altered by the polA1 mutation. When E. coli lysogenic cells superinfected with lambda were irradiated with doses sufficient to introduce at least seven breaks in the phage DNA, the chromosomal DNA and the superinfecting phage DNA sedimented similarly in alkaline sucrose gradients, indicating that both DNAs were broken to a similar extent during irradiation. However, the yield of breaks calculated for chromosomal DNA in similar experiments was greater than the yield calculated from the first break introduced into covalent circular lambda DNA molecules. These apparently contradictory results are explicable either if the initial break in a superhelical molecule occurs with an efficiency different from that for subsequent breaks, or if the pulsed electron radiation produces a high proportion of double-strand breaks.
