Thymineless mutagenesis in bacteriophage T4.

Thymine deprivation can be achieved in bacteriophage T4 either by the use of the thymidylate synthetase inhibitor FUdR, or by an appropriate combination of genetic blocks; both methods produce marked mutagenesis. Extensive tests of the specificity of thymineless mutagenesis reveal that only A:T base pairs are affected, and that transitions and possibly transversions are produced. This system therefore constitutes the first example of an A:T-specific mutagen. Thymineless mutagenesis in bacteriophage T4 exhibits a marked dependence upon the functional state of the DNA polymerase gene, but is largely independent of the px-y misrepair system.