and purification buy Y-27632 of covalently closed circular DNA (cccDNA) Covalently closed circular DNA containing a single 1,3-intrastrand d(GpTpG)-Cisplatin cross link (pt-GTG) was produced by priming 30 μg of plus strand M13 mp18 DNA modified to contain a sequence complementary to the platinated oligonucleotide within the polycloning site  with a 5-molar excess of 5′-phosphorylated platinated oligonucleotide in a 200-μl reaction mixture containing 10 mM Tris-HCl (pH7.9), 50 mM NaCl, 10 mM MgCl2, 1 mM DTT, 600 μM each of dATP, dCTP, dGTP and TTP, 2 mM ATP, 60 units of T4 DNA polymerase and T4 ligase (New England Biolab) for 4 h at 37°C. Closed circular DNA was isolated by CsCl/EtBr density gradient centrifugation and purified by consecutive butanol extraction, centrifugation in cetricon-10 microconcentrator (Amicon) and a Sephadex G-25 column (Sigma). DNA substrates were stored at 80°C in 10 mM Tris-HCl, 1 mM EDTA pH 8.0. Dual incision assay Ten μl reaction mixture contain 19 μg cell extract, 32 ng pt-DNA, 5 mM MgCl2, 40 mM HEPES-KOH pH 7.8, 0.5 mM Dithiothreitol, 2 mM ATP, 23 mM phosphcreatine, 18 μg bovine serum albumin (BRL, nuclease free). The reaction mixtures were incubated for a further 30 min. To analyze the release of DNA containing the lesion, a 34-mer oligonucleotide is used  as
a template by sequanase to incorporate radiolabeled dCTP on the 3′ end of the excised fragment then the excised labelled fragments were analyzed on 14% polyacrylamide gel. Selleckchem Anti-infection Compound Library Results HBx expression modulates the UV survival profile of Chang liver cells The effect of HBx expression on repair efficiency of a UV-damaged DNA in the human liver cell was monitored. HBx expressing plasmid pSBDR and a neomycin resistant plasmid pRC/CMV (control) were co-transfected into Chang liver cells. In the plasmid pSBDR, the HBx coding sequences are placed under the transcriptional control of native promoter and enhancer. pRC/CMV DNA was UV damaged for 2, 6, and 8 and 10 J/m2 of UV radiation. As a control, UV-damaged pRC/CMV DNA was co-transfected along with a plasmid pHEN100 lacking the coding
sequences of HBx. Cells were counted prior to co-transfection and selected in media containing G-418 for 2 weeks. Thereafter, G-418 resistant clones were counted. A decrease in the number of G-418 resistant clones per 105 cells was observed in HBx expressing cells PtdIns(3,4)P2 when compared with non-expressing cells (Figure 1). Figure 1 UV survival profile of HBx expressing human liver cells. HBx expression plasmid pSBDR and UV-damaged pRC/CMV were co transfected into chang liver cells. Plates were incubated in dark for 2 weeks in the presence of G418. The number of G418 resistant cells per 105 cells is plotted. Live cells were counted by staining with trypan blue prior to transfection. The ordinate represents the survival fraction, while the abscissa displays the dosage of UV irradiation. Each bar represents Mean ± S.D.