SCEs are induced by replication of BrdU-substituted DNA templates, but not by incorporation of BrdU into nascent DNA |
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Authors: | D G Stetka M C Spahn |
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Institution: | Laboratoire de Biologie Cellulaire et Génétique, Bâtiment 400, Université Paris-Sud, Centre d''Orsay, 91405 Orsay-Cedex France |
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Abstract: | After 3 rounds of DNA replication in the presence of BrdU, third-division metaphase cells can be scored for the frequencies of SCEs that occurred during cycles 1 and 2, and also for the frequency of SCE during cycle 3. This procedure was used to resolve the issue of SCE induction by replication of BrdU-substituted DNA templates versus induction by BrdU incorporation into nascent DNA. It was observed that third-cycle SCE frequencies in CHO are dependent upon the amount of BrdU that was present during cycles 1 and 2 and are independent of the BrdU concentration during the third cycle. It is therefore BrdU serving as a template, rather than BrdU being incorporated, that initiates the SCE event. A model is proposed that produces reasonable fits to the observed data. It also predicts a true background or spontaneous SCE frequency of 3 per cell per cycle as previously reported by Heartlein et al. (Mutation Res., 107 (1983) (103-109). The predicted single twin ratio is higher than that reported by Wolff and Perry (Exp. Cell Res., 93 (1975) 23-30), and possible explanations for this discrepancy are discussed. |
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Keywords: | MNNG DWAG defective white ascospore group |
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