A NEW MODEL DESCRIBING THE CURVES FOR REPAIR OF BOTH DNA DOUBLE-STRAND BREAKS AND CHROMOSOME-DAMAGE

A review of reports dealing with fittings of the data for repair of DN A double-strand breaks (DSBs) and excess chromosome fragments (ECFs) s hows that several models are used to fit the repair curves, Since DSBs and ECFs are correlated, it is worth developing a model describing bo th phenomena. The curve-fitting models used most extensively, the two repair half-times model for DSBs and the monoexponential plus residual model for ECFs, appear to be too inflexible to describe the repair cu rves for both DSBs and ECFs, We have therefore developed a new concept based on a variable repair half-time, According to this concept, the repair curve is continuously bending and dependent on time and probabl y reflects a continuous spectrum of damage repairability, The fits of the curves for DSB repair to the variable repair half-time and the var iable repair half-time plus residual models were compared to those obt ained with the two half-times plus residual and two half-times models, Similarly, the fits of the curves for ECF repair to the variable repa ir half-time and variable half-time plus residual models were compared to that obtained with the monoexponential plus residual model. The qu ality of fit and the dependence of adjustable parameters on the portio n of the curve fitted were used as comparison criteria. We found that: (a) It is useful to postulate the existence of a residual term for un repairable lesions, regardless of the model adopted. (b) With the two cell lines tested (a normal and a hypersensitive one), data for both D SBs and ECFs are best fitted to the variable repair half-time plus res idual model, whatever the repair time range. (C) 1996 by Radiation Res earch Society