Streptococcus gordonii Strains Resistant to Fluorodeoxyuridine Contain Mutations in the Thymidine Kinase Gene and Are Deficient in Thymidine Kinase Activity

Mutants of Streptococcus gordonii resistant to 5-fluorodeoxyuridine (FUdR(r)) were isolated. Each strain contained a point mutation resulting in the premature termination of the thymidine kinase (TK) open reading frame (tdk). In vitro translation of the mutant tdk coding regions resulted in synthesis of truncated TK polypeptides deficient in TK activity.