Inactivation by nitrogen mustard of plasmids introduced into normal and Fanconi's anaemia cells

An SV40-transformed Fanconi's anaemia (FA) cell line, GM6914, exhibits approximately 2.4-fold increased sensitivity to the cytotoxic effects of nitrogen mustard (NM) when compared with the normal line, MRC5-V1. Host cell reactivation of NM-treated plasmid has been investigated using transient expression vectors which contain the chloramphenicol acetyltransferase (CAT) gene. In both cell types there is a similar, dose-dependent reduction in CAT expression which correlates with an increase in NM-induced DNA-interstrand crosslinking. The data are consistent with two possible mechanisms for inactivation of the plasmid. Either a single crosslink anywhere within the plasmid is sufficient to prevent transcription of the cat gene. Alternatively, inactivation may result from some other more prevalent NM-induced lesions within the cat coding sequence.