Untransformed xeroderma pigmentosum cells are not hypersensitive to sister-chromatid exchange production by ethyl methanesulphonate--implications for the use of transformed cell lines and for the mechanism by which SCE arise.

A transformed cell line, XP12RO(SV40) has previously been found to be hypersensitive to several chemical mutagens including ethyl methanesulphonate, as judged by sister-chromatid exchange (SCE) formation. The hypersensitivity of this line has been confirmed for SCE formation and extended to cell survival. Measurements of SCE formation and survival show, however, that the hypersensitivity of the XP12RO(SV40) cell line is not typical of the primary strain (XP12RO) from which the transformed line was derived, nor it is typical of other primary strains also belonging to complementation group A (XP4LO, XP25RO). These results suggest that reports based on single cell lines must be viewed with caution and that the relationship between unexcised damage in DNA and SCE production is uncertain.