Objective         To investigate the feasibility of using circular rolling circle amplification (RCA) to detect the resistance gene to tenofovir in hepatitis B virus (HBV).        Methods         The mutation site of resistance gene of HBV to tenofovir was taken as target to design the padlock probe. Wild and mutation templates were also synthesized in this research. The designed padlock probes were linked to closed rings by E.coli DNA ligase when they specifically bonded to wild templates. RCA was started when primers annealed to the probes. Then HpaⅠ  cut off the product drastically

and more templates were released. Then the processes above were repeated to start the RCA for a second time. Finally the product was detected by 1% agarose electrophoresis. The influential factors of ligation efficiency

specificity and sensitivity were also studied.       Results         The ligation efficiency and specificity of the probe were enhanced when the hybridization temperature was set at 45 ℃. Among the different concentrations of wild template detected

the lowest rate of RCA was 50 pmol/L

and it was as lower as 5 pmol/L when the circular RCA was used.       Conclusion         Circular RCA is established successfully to detect resistance gene of HBV to tenofovir.