In vivo fate of MMS-induced DNA lesions that elicit SCE.

A previously reported in vivo protocol, which uses three-way differential staining (TWD) of sister chromatids, allows the screening of mutagen-induced sister-chromatid exchange (SCE) in each of the two cell divisions after mutagen treatment and also those occurring at apparently the same locus in both divisions. In the present work the effect of methyl methanesulfonate (MMS) was studied by means of this protocol. The results showed that MMS-induced DNA lesions that cause SCE are persistent. Some lesions were induced in the second division, as was inferred from the analysis of the response in single cells. The data also indicate that bromodeoxyuridine reduces DNA sensitivity to SCE induction by MMS.