Differences in the ability of human lymphoblastoid lines to exclude bromodeoxyuridine and in their sensitivity to methyl methanesulfonate and to incorporated [3H]thymidine.

Six Burkitt's lymphoma-derived lines were more resistant to methyl methanesulfonate than were six lymphoblastoid lines derived by in vitro transformation as measured by cloning ability in soft agar. The differences were due to cell response rather than to reactivity. Lymphoblastoid lines were also more sensitive to [3H]thymidine incorporated along with bromodeoxyuridine than were the lymphoma lines tested. All lines showed excision repair activity as measured by the benzoylated napthoylated DEAE cellulose method, although there were quantitative differences in the activity of different lines. Most lymphoblastoid lines synthesize DNA of lower density when incubated in analog-containing medium due to their ability to discriminate against bromodeoxyuridine and to select for thymidine in a mixture. All the lymphoma cell lines tested were unable to discriminate between thymidine and bromodeoxyuridine. The ability of lymphoma cells to produce large quantities of dense radioactive, doubly substituted DNA when incubated in medium with bromodeoxyuridine and thymidine is due to their inability to discriminate between nucleosides and to their resistance to incorporated [3H]thymidine.