Flap endonuclease 1 is involved in cccDNA formation in the hepatitis B virus
Fig 6
FEN1 protein facilitates cccDNA formation in vitro.
(A) Schematic presentation of in vitro cccDNA formation assay. Purified NC-DNA (108 copies) was incubated with recombinant FEN1, Bst DNA polymerase, and Taq DNA ligase. Following incubation, the DNA was purified and analyzed (B–F). Regions for qPCR amplification (E and F) were indicated as p. The 5.4-kb PstI fragment in HBV plasmid (Control) has a partial HBV sequence but does not have core and intact P genes. (B) cccDNA-selective qPCR. Each result represents the mean ± SEM of three independent experiments. Asterisks indicate statistically significant differences; ***P < 0.001 compared with negative control (no enzyme). (C) Southern blot analysis of in vitro cccDNA formation assay. The DNA was analyzed directly (left), or treated with T5 exonuclease (middle) or T5 exonuclease, then subsequently digested with EcoRI (right). (D) Detection of RCA products. DNA treated with indicated enzymes was subjected to RCA and then digested with indicated restriction enzymes. Arrow indicates the 5.4-kb fragment of the HBV plasmid, used as a replication-defective control for transfection in E and F. (E and F) Equal amounts of digested RCA product generated in (D) were self-circularized and then transfected into HepG2 cells. Three days after transfection, HBV DNA was analyzed by qPCR. Each result represents the mean ± SEM of three independent experiments. Asterisks indicate statistically significant differences compared with the control; * P < 0.05, ** P < 0.01.