Analysis of non-linearities in frequency curves for UV-induced mitotic recombination in wild-type and excision-repair-deficient strains of yeast |
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Authors: | B A Kunz F Eckardt R H Haynes |
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Institution: | 1. Biology Department, York University, 4700 Keele Street, Toronto, Ont. M3J 1P3 Canada;2. Gesellschaft fur Strahlen - und Umweltforschung, Abteilung Strahlenbiologie, D-8042 Neuherberg F.R.G. |
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Abstract: | Frequency curves for UV-induced mitotic recombination often are linear at low doses. As dose increases, these curves either increase at higher powers of dose and/or reach a maximum induced frequency and then decline. Similar dose-response patterns have been observed previously for mutation. The non-linearities can arise from higher order effects inherent in the molecular mechanisms of mutagenesis and/or from 'delta-effects' (Eckardt and Haynes, 1977a), i.e., differential probabilities of clone formation for mutant and non-mutant cells. Previously, we have shown that one can distinguish between these two possibilities by plotting the ratio of the induced mutant yield to the linear component of frequency as a function of dose (Haynes et al., 1985). In this study, we have used this ratio, a quantity we call 'apparent survival', to analyse the non-linear regions of the dose-response curves for UV-induced mitotic crossing-over and gene conversion in wild-type (RAD) and excision-repair-deficient (rad3) strains of yeast. Plots of apparent survival versus dose reveal the existence of a positive, non-linear component associated with UV-induced gene conversion in RAD, but not rad3, cells. A high dose decline in frequency, which is observed for UV-induced recombination in both strains, can be attributed to delta-effects. |
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