Ability of various alkylating agents to induce adaptive and SOS responses: A study with lacZ fusion

We used alkA′-lacZ′ and umuC′-lacZ′ fused genes and determined the ability of various alkylating agents to induce adaptive and SOS responses. The degree of induction of expression of these genes was quantitatively measured by a simple colorimetric assay of ß-galactosidase activity. S_N1 type methylating agents, such as N-methyl-N′-nitro-N-nitrosoguanidine and B-methyl-N-nitrosourea, were more effective inducers for the alkA than for the umuC system, while S_N1 type ethylating agents, such as N-ethyl-N′-nitro-N-nitrosoguanidine and N-ethyl-N-nitrosourea, were more potent inducers for the umuC than for the alkA system. Similar but less striking effects on the two systems were obtained with S_N2 type alkylating agents.