Inhibitor studies of phage T4 wild-type and mutant DNA polymerase. IV. The substrate analog 3′-fluorothymidine 5′-triphosphate

The deoxythymidine5′-triphosphate (dTTP) analog 3′-fluorothymidine 5′-triphosphate (3′-FdTTP) inhibits DNA synthesis by T4 wild-type, L98 (mutator) and CB121 (antimutator) DNA polymerase. CB121 DNA polymerase is less sensitive by a factor of two than the L98 and T4⁺ enzymes. Inhibition is not due to incorporation of the analog into DNA. 3′-FdTTP acts competitively to the substrate dTTP. The CB121 polymerase exhibits a higher K_i to K_m ratio than the other two enzymes (5.3 vs. 3.3) and thus discriminates better between the substrate dTTP and its analog 3′-FdTTP. 3′-FdTTP inhibits the polymerase-associated 3′-5′ exonuclease activities to the same extent as their polymerase activities. The CB121 3′-5′ exonuclease activity is suppressed only half as much by 3′-FdTTP as by dTTP. The results are discussed in relation to the role of T4 DNA polymerase and its associated 3′-5′ exonuclease in determining the accuracy of DNA replication.