A NEW SALMONELLA-TYPHIMURIUM NM5004 STRAI N EXPRESSING RAT GLUTATHIONE-S-TRANSFERASE-5-5 - USE IN DETECTION OF GENOTOXICITY OF DIHALOALKANES USING AN SOS UMU TEST SYSTEM/

The Escherichia coli mu operon was subcloned into a pKK233-2 vector co ntaining rat glutathione S-transferase (GST) 5-5 cDNA and the plasmid thus obtained was introduced into Salmonella typhimurium TA1535. The n ewly developed strain S.typhimurium NM5004, was found to have 52-fold greater GST activity than the original umu strain S.typhimunrium TA153 5/pSK1002. We compared sensitivities of these two tester strains, NM50 04 and TA1535/ pSK1002, for induction of umuC gene expression with sev eral dihaloalkanes which are activated or inactivated by GST 5-5 activ ity. The induction of umuC gene expression by these chemicals was moni tored by measuring the cellular beta-galactosidase activity produced b y umuC '' lacZ fusion gene in these two tester strains. Ethylene dibro mide, 1-bromo-2-chloroethane, 1,2-dichloroethane, and methylene dichlo ride induced umuC gene expression more strongly in the NM5004 strain t han the original strain, 4-Nitro-quinoline 1-oxide and N-methyl-N'-nit ro-N-nitrosoguanidine were found to induce umuC gene expression to sim ilar extents in both strains. In the case of 1-nitropyrene and 2-nitro fluorene, however, NM5004 strain showed weaker umuC gene expression re sponses than the original TA1535/pSK1002 strain, 1,2-Epoxy-3-(4'-nitro phenoxy)propane, a known substrate for GST 5-5, was found to inhibit u muC induction caused by 1-bromo-2-chloroethane. These results indicate that this new tester NM5004 strain expressing a mammalian GST theta c lass enzyme may be useful for studies of environmental chemicals propo sed to be activated or inactivated by GST activity.