Home About us Contact
|
Home About us Contact | ||
|
|
||
G Residues (g + residue)
Selected AbstractsHCV RNA-dependent RNA polymerase replicates in vitro the 3, terminal region of the minus-strand viral RNA more efficiently than the 3, terminal region of the plus RNAFEBS JOURNAL, Issue 22 2001Sandrine Reigadas The NS5B protein, or RNA-dependent RNA polymerase of the hepatitis virus type C, catalyzes the replication of the viral genomic RNA. Little is known about the recognition domains of the viral genome by the NS5B. To better understand the initiation of RNA synthesis on HCV genomic RNA, we used in vitro transcribed RNAs as templates for in vitro RNA synthesis catalyzed by the HCV NS5B. These RNA templates contained different regions of the 3, end of either the plus or the minus RNA strands. Large differences were obtained depending on the template. A few products shorter than the template were synthesized by using the 3, UTR of the (+) strand RNA. In contrast the 341 nucleotides at the 3, end of the HCV minus-strand RNA were efficiently copied by the purified HCV NS5B in vitro. At least three elements were found to be involved in the high efficiency of the RNA synthesis directed by the HCV NS5B with templates derived from the 3, end of the minus-strand RNA: (a) the presence of a C residue as the 3, terminal nucleotide; (b) one or two G residues at positions +2 and +3; (c) other sequences and/or structures inside the following 42-nucleotide stretch. These results indicate that the 3, end of the minus-strand RNA of HCV possesses some sequences and structure elements well recognized by the purified NS5B. [source] Xis protein of the conjugative transposon Tn916 plays dual opposing roles in transposon excisionMOLECULAR MICROBIOLOGY, Issue 6 2001Douglas Hinerfeld The binding of Tn916 Xis protein to its specific sites at the left and right ends of the transposon was compared using gel mobility shift assays. Xis formed two complexes with different electrophoretic mobilities with both right and left transposon ends. Complex II, with a reduced mobility, formed at higher concentrations of Xis and appeared at an eightfold lower Xis concentration with a DNA fragment from the left end of the transposon rather than with a DNA fragment from the right end of the transposon, indicating that Xis has a higher affinity for the left end of the transposon. Methylation interference was used to identify two G residues that were essential for binding of Xis to the right end of Tn916. Mutations in these residues reduced binding of Xis. In an in vivo assay, these mutations increased the frequency of excision of a minitransposon from a plasmid, indicating that binding of Xis at the right end of Tn916 inhibits transposon excision. A similar mutation in the specific binding site for Xis at the left end of the transposon did not reduce the affinity of Xis for the site but did perturb binding sufficiently to alter the pattern of protection by Xis from nuclease cleavage. This mutation reduced the level of transposon excision, indicating that binding of Xis to the left end of Tn916 is required for transposon excision. Thus, Xis is required for transposon excision and, at elevated concentrations, can also regulate this process. [source] Chemopreventive Action of Xanthone Derivatives on Photosensitized DNA Damage,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Kazutaka Hirakawa ABSTRACT Photosensitized DNA damage participates in solar-UV carcinogenesis, photogenotoxicity and phototoxicity. A chemoprevention of photosensitized DNA damage is one of the most important methods for the above phototoxic effects. In this study, the chemopreventive action of xanthone (XAN) derivatives (bellidifolin [BEL], gentiacaulein [GEN], norswertianin [NOR] and swerchirin [SWE]) on DNA damage photosensitized by riboflavin was demonstrated using [32P]-5,-end-labeled DNA fragments obtained from genes relevant to human cancer. GEN and NOR effectively inhibited the formation of piperidine-labile products at consecutive G residues by photoexcited riboflavin, whereas BEL and SWE did not show significant inhibition of DNA damage. The four XAN derivatives decrease the formation of 8-oxo-7,8-dihydro-2,-deoxyguanosine (8-oxodGuo), an oxidative product of G, by photoexcited riboflavin. The preventive action for the 8-oxodGuo formation of these XAN derivatives increased in the following order: GEN > NOR , BEL > SWE. A fluorescence spectroscopic study and ab initio molecular orbital calculations suggested that the prevention of DNA photodamage is because of the quenching of the triplet excited state of riboflavin by XAN derivatives through electron transfer. This chemoprevention is based on neither antioxidation nor a physical sunscreen effect; rather, it is based on the quenching of a photosensitizer. In conclusion, XAN derivatives, especially GEN, may act as novel chemopreventive agents by the quenching mechanism of an excited photosensitizer. [source] Oxidative DNA Damage Induced by a Metabolite of 2,Naphthylamine, a Smoking-related Bladder CarcinogenCANCER SCIENCE, Issue 7 2002Shiho Ohnishi 2-Naphthylamine (2-NA), a bladder carcinogen, is contained in cigarette smoke. DNA adduct formation is thought to be a major cause of DNA damage by carcinogenic aromatic amines. We have investigated whether a metabolite of 2-NA, 2-nitroso-1-naphthol (NO-naphthol) causes oxidative DNA damage, using 32P-labeled DNA fragments. We compared the mechanism of DNA damage induced by NO-naphthol with that by N -hydroxy-4-aminobiphenyl (4-ABP (NHOH)), a metabolite of 4-aminobiphenyl, another smoking-related bladder carcinogen. NO-naphthol caused Cu(II)-mediated DNA damage at T>C>G residues, with non-enzymatic reduction by NADH. Catalase and bathocuproine, a Cu(I)-specific chelator, inhibited the DNA damage, suggesting the involvement of H2O2 and Cu(I). Some free ·OH scavengers also attenuated NO-naphthol-induced DNA damage, while free ·OH scavengers had no effect on the DNA damage induced by 4,ABP(NHOH). This difference suggests that the reactive species formed by NO-naphthol has more free ·OH- character than that by 4,ABP(NHOH). A high-pressure liquid chromatograph equipped with an electrochemical detector showed that NO-naphthol induced 8,oxo,7,8,dihydro,2,,deoxyguanosine formation in the presence of NADH and Cu(II). The oxidative DNA damage by these aminoaromatic compounds may participate in smoking-related bladder cancer, in addition to DNA adduct formation. [source] | ||||||||||