title: Benzo[a]pyrene-DNA adducts inhibit the DNA helicase activity of the bacteriophage T7 gene 4 protein.
abstract: The gene 4 protein of bacteriophage T7 provides the essential helicase and primase activities for the replication of the T7 genome. In addition, it also displays a DNA-dependent deoxyribonucleoside triphosphatase activity, the preferred substrate of which is dTTP. Previous investigations have demonstrated that the translocation of the gene 4 protein along single-stranded DNA is blocked by the presence of benzo[a]pyrene-DNA adducts and that the gene 4 protein is likely to be sequestered at the sites of these adducts. In the present study, we directly show that the helicase activity of the gene 4 protein is also profoundly inhibited by the benzo[a]pyrene-DNA adducts. The inhibitory effects of these adducts are strand-specific in that they block the DNA helicase activity of the gene 4 protein only when they are located in the DNA strand where the gene 4 protein translocates when it unwinds double-stranded DNA. Consistent with the hypothesis that the gene 4 protein is sequestered at the adduct site, we also show that the complexes formed by the gene 4 protein and benzo[a]pyrene-modified DNA are far more stable than those formed by the gene 4 protein and unmodified DNA.
authors.affiliation: Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Yong
authors.forename: L J
authors.initials: LJ
authors.lastname: Romano
mesh_terms: D017123:Bacteriophage T7 / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000633:toxicity*; D018736:DNA Adducts / Q000235:genetics / Q000633:toxicity*; D004249:DNA Damage; D004265:DNA Helicases / Q000037:antagonists & inhibitors*; D019915:DNA Primase; D004277:DNA, Single-Stranded / Q000187:drug effects; D004355:Drug Stability; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000187:drug effects / Q000235:genetics; D009994:Osmolar Concentration; D012316:RNA Nucleotidyltransferases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D018736:DNA Adducts; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D001564:Benzo(a)pyrene; D019915:DNA Primase; D012316:RNA Nucleotidyltransferases; C027093:TraI protein, E coli; D004265:DNA Helicases