dUTP and dCTP derivatives containing a 4 azido 2,3,5,6 tetrafluorobenzylideneaminooxy group were incorporated into the 3´ end of the DNA primer within complexes with the DNA matrix as analogs of natural dTTP by virtue of catalytic activity of DNA polymerase β or endogenous DNA polymerases of the cell extract. The photoreactive DNAs synthesized in situ were used for affinity modification of DNA polymerase β and DNA binding proteins of the cell extract. For the photoreactive DNA based on these analogs, the efficiency of formation of covalent adducts with DNA polymerase β under the highest degree of DNA complexation with the enzyme was determined. The yield of covalent DNA adducts with the enzyme was 28-47%, depending on the type of the analog. The effect of the sequence of the DNA template near the localization of the photoreactive group on the redistribution of covalent cross links between the possible targets was demonstrated. A possibility of increasing the efficiency of DNA poly merase β modification in the presence of a substantial excess of photoreactive DNA using a sensitizer, a dUTP derivative containing a pyrene residue, was studied. When photoreactive DNA containing a 2,3,5,6 tetrafluoro 4 azidobenzoyl (FAB) group was used, about 60% of DNA polymerase β was covalently attached to DNA. Photoreactive dNTP analogs ensuring a high level of protein modification in the cell extract were found.Previously, 1-4 we performed a number of compara tive studies of the efficiency of formation of photo induced adducts in primer-template complexes of DNA polymerase β and DNA polymerase of Thermus thermophilus. As the photoaffinity reagents, we used DNA primers containing various arylazido groups incorporated into heterocyclic bases at the 3´ end nucleotide. The high est efficiency (~30%) of covalent cross linking of pho tolysis products of this type of primers with other compo nents of the complexes was attained with the 4 (4 azido 2,3,5,6 tetrafluorobenzylideneaminooxy)butoxy (FABO) and 4 azido 2,5 difluoro 3 chloropyridin 6 yl 1 (FAP) groups. 2 A comparative study of the visible light sensi tized photomodification of the primer-template com plex with DNA polymerase β in the presence of АТР derivatives bearing sensitizing groups attached to the γ phosphate was also carried out. 4 It was found that the total efficiency of cross linking and the distribution of the cross links among components of the complexes de pend crucially on their structures (the sequence of the primer-template duplex, the structure of the sensi tizer, etc.) and irradiation conditions. A number of studies 5-7 demonstrated the possibility of conducting sensitized photomodification using 5 substituted dUTP-pyrene derivatives as the sensitizers.This work aims at further development of the design of affinity photoreagents to study the composition and struc ture of macromolecular replication and repair protein complexes in reconstructed systems and cell extracts and, in the future, in vivo. To this end, we performed a number of studies aimed at increasing ...