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Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=irab20 International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine ISSN: 0020-7616 (Print) (Online) Journal homepage: www.tandfonline.com/journals/irab19 The Effect of Prior Ultra-violet Irradiation on X-ray- induced Inhibition of Mammalian DNA-synthesis Robert B. Painter To cite this article: Robert B. Painter (1968) The Effect of Prior Ultra-violet Irradiation on X-ray-induced Inhibition of Mammalian DNA-synthesis, International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine, 13:3, 293-295, DOI: 10.1080/09553006814550241 To link to this article: https://doi.org/10.1080/09553006814550241 Published online: 03 Jul 2009. Submit your article to this journal Article views: 101 View related articles https://www.tandfonline.com/action/journalInformation?journalCode=irab20 https://www.tandfonline.com/journals/irab19?src=pdf https://www.tandfonline.com/action/showCitFormats?doi=10.1080/09553006814550241 https://doi.org/10.1080/09553006814550241 https://www.tandfonline.com/action/authorSubmission?journalCode=irab20&show=instructions&src=pdf https://www.tandfonline.com/action/authorSubmission?journalCode=irab20&show=instructions&src=pdf https://www.tandfonline.com/doi/mlt/10.1080/09553006814550241?src=pdf https://www.tandfonline.com/doi/mlt/10.1080/09553006814550241?src=pdf INT. J. RADIAT. BIOL., 1967, VOL. 13, NO. 3, 293 -295 The effect of prior ultra-violet irradiation on X-ray-induced inhibition of mammalian DNA-synthesist ROBERT B. P A I N T E R Laboratory of Radiobiology, University of California Medical Center, San Francisco, California (Received 5 December 1967) Irradiation with either ultra-violet light (u.v.) or x-rays depresses the incor- poration of radioactive precursors into HeLa DNA (Rasmussen and Painter 1964, Painter and Rasmussen 1964). In either case a plot of the dose response of incorporation yields a curve with at least two components, the first of which is relatively steep at low doses, followed by a shallower component at higher doses. The curves are by no means identical, however; the steep component is much more prominent in the ultra-violet than in the x-ray curves. The question arises whether the mechanism of inhibition is the same in both eases. To try to answer it, we performed experiments in which HeLa cultures were irradiated first with a single dose of o.v., then with graded doses of x-rays, and the effect on incorporation of thymidine into DNA was measured. The results show that prior ultra-violet irradiation does not alter appreciably the shape of the x-ray, dose-response curve. Growth of HeLa cells in Vycor flasks and ultra-violet irradiations w e r e carried out as previously reported (Rasmussen and Painter 1964), except that the latter was performed in the anteroom of an x-ray unit. Immediately after irradiation with o.v. (a single dose), graded doses of x-ray were administered to the same flasks and to equal numbers that had not been o.v.-irradiated. X-irra- diations were performed as previously described (Painter and Rasmussen 1964), using 300 kvp x-rays, at a dose-rate of 200-300 R/min, under conditions of minimal scatter. Some cultures were irradiated with u.v. only, some with x-rays only, and some not irradiated at all. Two to four flasks for each treatment group were used. Incubations for 1-2 hours with 3H-thymidine (1/~Ci/ml, 6.7 Ci/mM, New England Nuclear Corp.) followed the irradiations. The DNA was then extracted and the specific activity determined (Painter and Rasmussen 1964). In most cases the range of the values was smaller than the width of the symbols representing their mean in the figure. The important result of these experiments is the observation that prior irradiation with v.v. fails to abolish the steep component of the x-ray, dose- response curve. This is true even at a point where the u.v. alone has depressed the uptake of thymidine to less than 10 per cent of control. (In this experiment the range was less than 5 per cent of the mean of all points). t Work performed under the auspices of the U.S. Atomic Energy Commission. 294 Correspondence The most important effect of u.v. on DNA is damage to pyrimidine bases leading to dimer formation (Setlow 1966). This lesion inhibits the rate of DNA- synthesis in bacteria (Swenson and Setlow 1966) and in in vitro mammalian systems (Bollum and Setlow 1963), although it alone may not be responsible for the inhibition of DNA-synthesis in mammalian cells in vivo (Cleaver 1967). Regardless of the specific lesion responsible for u.v. inhibition of mammalian DNA-synthesis, the results presented here show that it overlaps very little with the one(s) causing the steep depression of synthesis by low doses of x-rays. 1.0 0,8 0.6 E 0.4 u z 0.3 G z 0 .2 0 u z _o 0.1q 0.08 0.06 ~ ~ ~ ~ ~ l ~ y alone lOOergs 4- X-Ray 8 = ._.~A I i I 2 a :X-Ray only 800ergs ÷ X-Ray I I / I 3 4 5 6 K RAD o =X-Ray only Exp. I • :UV + X-Ray Exp. 3 • =UV + X-Ray =X-Ray only Exp. 4 °. =X-Ray only Exp. 2 • =UV + X-Ray • :UV + X-Ray Inhibition of incorporation of ~H-thymidine by x-rays with and without prior v.v.-irradia- tion. All incorporations were measured as c.p.m.//~g DNA, based on 1-6 x 104 total counts per sample. We previously showed that DNA itself is a component of the system that is affected by low doses of x-radiation (Painter and Rasmussen 1964). Since the steep depression occurs at low doses, we inferred that a very large target is involved, and suggested that a DNA-replicating unit of the order of 109-10 TM daltons is the component responsible for maintaining the normal rate of DNA- synthesis in the cell. A ' h i t ' in this component somehow disorganizes the system in such a way that the rate of synthesis is greatly reduced. It appears that action of u.v. does not disorganize the DNA-replicating units, even after a great deal of base damage has occurred in them. Therefore the x-ray lesion causing the disorganization of the DNA-replicating unit probably is not asso- ciated with base damage. A primary action of ionizing radiation is believed to be strand breaks (Freifelder 1966), which are rarely, if ever, induced by u.v. Freifelder and Davison 1963). Since single-strand breaks apparently can be annealed rapidly by mammalian cells (Lett, Caldwell, Dean and Alexander 1967), the x-ray lesion responsible for the disorganization is more likely to be a double- strand break, possibly brought about by two single-strand events close enough in distance and time to cause a disruption in the linear continuity of the DNA molecule. Correspondence 295 REFERENCES BOLLUM, F. J., and S•TLOW, R. B., 1963, Biochim. biophys. Acta, 68, 599, CI~AWa, J. E., 1967, Radiat. Res., 30, 795. F~I~I~DEa, D., 1966, Radiat. Res., 29, 329. F~IFELD~a, D., and DAvlso~, P. F., 1963, Biophys. ft , 3, 97. LETT, J. T., C~UDW~LL, I., DEW, C. J., and AI~X.~DEa, P., 1967, Nature, Lond., 214, 790. PAINTER, R. B., and RASMUSSEN, R. E., 1964, Nature, Lond., 201, 162. RASMUSSEn, R. E., and PAINTER, R. B., 1964, Nature, Lond., 203, 1360. SETLOW, R. B., 1966, Science, N. Y., 153, 379. SWANSON, P. A., and SETLOW, R. B., 1966, ft. molec. Biol., 15, 201.
