Analysis of the role of 5' regulatory mutations in the activation of quiescent metallothionein genes after carcinogen treatment.

S49 are mouse thymic lymphoma cells which do not express the two closely linked mouse metallothionein (MT) genes; however, previous studies demonstrated that treatment of S49 cells with chemical carcinogens or ultraviolet irradiation can activate these quiescent genes. To determine if activation of MT-I or MT-II in these variants is a result of cis-acting mutations, we amplified and sequenced the immediate 5' regions of 19 cadmium resistant S49 variants: MT-I+/MT-II-, MT-I-/MT-II+, MT-I+/MT-II+, and MT-I-/MT-II-. None of the variants contained mutations in the analyzed regions. Thus, the observed changes in MT expression must result from mutations at other sites or from non-mutational mechanisms.