A binary system of photoaffinity reagents was proposed earlier for highly efficient labeling of DNA polymerases by 5;-[32P]DNA primers. In the present study we demonstrate the feasibility of this approach to increase the efficiency of DNA polymerase labeling. A photoactive 2,3,5,6-tetrafluoro-4-azidobenzoyl (FAB) group was incorporated at the 3;-end of 5;-[32P]DNA primers synthesized by DNA polymerase beta or Tte in the presence of one of the dTTP analogs--FAB-4-dUTP, FAB-9-dUTP, or FAB-4-ddUTP. The reaction mixture was irradiated by light with wavelength of 334-365 nm (direct labeling) or 365-450 nm in the presence of photosensitizer, one of dTTP analogs containing a pyrene moiety, Pyr-6-dUTP or Pyr-8-dUTP. In the case of the binary system of photoaffinity reagents, a FAB group is activated by energy transfer from sensitizer localized in the dNTP-binding site of DNA polymerase in the triple complex, comprised by reagent, DNA polymerase, and Pyr-6(8)-dUTP. Direct activation of the FAB group under these conditions is negligible. The most efficient photolabeling of DNA polymerases was observed with a primer containing a FAB-4-dUMP group at the 3;-end, and Pyr-6-dUTP as a photosensitizer. Using 10-fold molar excess of photoreagent to DNA polymerase beta, the labeling efficiency was shown to achieve 60%, which is 2-fold higher than the efficiency of the direct DNA polymerase labeling under harsher conditions (334-365 nm).