Mechanism of caffeine-induced inhibition of DNA synthesis in Escherichia coli

Caffeine inhibited DNA synthesis in toluene-treated Escherichia coli K 12 strains to the same extent as in intact cells using the incorporation of [ 3H]thymidine as a measure of DNA synthesis. The inhibition was found to be competitive with ATP, and it was not influenced by the concentrations of deoxynucleoside triphosphates to any extent. When caffeine was added together with other DNA synthesis inhibitors such as novobiocin, nalidixic acid or actinomycin D, the inhibition in all cases was non-additive. It is suggested that caffeine inhibits one of the ATP-requiring enzymes in the DNA replication machinery, possibly DNA polymerase III or one of the DNA helicases.