<正> Objective: To screen a triple helix-forming oligodeoxyribonucleotide （TFO） that can bind HBV core promoter at target site with high affinity and specificity

and to observe the ability of manganese porphyrin modified TFO to combine and cleave HBV DNA. Methods: Similar homopurine domain （1 734 - 1 754） in HBV core promoter was selected as target sequence. Several corresponding TFOs were synthesized. The affinities and specificities of TFOs binding target sequence were tested with electrophoretic mobility shift and DNase I footprinting assays. The selected best TFO was modified with manganese porphyrin and acridine. The ability of the TFO derivative to cleave HBV DNA was observed with cleavage experiment. Results: Under the condition of 371 and pH 7. 4

the TFO consisting of cytidylate and thymidylate （CT-TFO） and the parallel TFO consisting of guanylate and thymidylate （GT-TFOp） bound the target sequence weakly with Kd values much more than 10 -6 mol/L. The affinities of anti-parallel GT-TFO （ GT-TFOap）