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5-Bromouracil-Tolerant Mutants of Bacillus subtilis

^a Department of Biology, Princeton University, Princeton, New Jersey 08540

ABSTRACT

5-Bromouracil (BU)-tolerant mutants of Bacillus subtilis 23 (thy his) have been isolated. Several classes of tolerant mutants were obtained by a sequential selection procedure. The classes can be distinguished by their relative BU tolerance as well as several other phenotypic characteristics. The mutants can grow for an extended period of time in minimal medium supplemented with amino acids and BU, in which the sensitive parental strain (Bu⁺) undergoes rapid cell death. Both mutants But-1 and But-1310 have a greater rate of deoxyribonucleic acid (DNA) synthesis by a factor of two in the presence of BU than Bu⁺, But-1 being somewhat faster than But-1310. The preferential incorporation of thymine to BU of But-1 is about half that of the Bu⁺ strain during DNA replication in minimal medium supplemented with 10 µg of BU/ml and 1 µg of thymine/ml. It is not known at what step or steps this reduction in selectivity occurs.

¹ Present address: Division of Biology, California Institute of Technology, Pasadena, Calif. 91109.