title: Triple-helix specific ligands stabilize H-DNA conformation.
abstract: Under superhelical stress, oligopurine-oligopyrimidine mirror-repeat sequences are able to adopt H-DNA conformations where a triple-helical and a single-stranded structure co-exist. We have previously shown that a benzo[e]pyridoindole derivative (BePI), an antitumor drug interacting more tightly with triplex than with duplex DNA, strongly stabilizes intermolecular triple helices formed upon binding of homopyrimidine oligonucleotides to the major groove of double-stranded DNA at oligopurine-oligopyrimidine sequences. Here we show that an intramolecular triple helix is also strongly stabilized by this ligand. In vitro elongation performed by different DNA polymerases (bacteriophage T7, Escherichia coli or Taq polymerase) could be irreversibly inhibited by the H-DNA structure in the presence of BePI. A mirror-repeat polypurine-polypyrimidine sequence inserted between the E. coli beta-lactamase gene (conferring ampicillin resistance) and its bla promoter strongly inhibited transcription of the beta-lactamase gene in vivo. In the absence of supercoiling, transition to the H-conformation did not occur, but BePI stabilized the H-DNA structure induced by supercoiling as shown by chemical probes (chloroacetaldehyde). The results presented here open a new field of investigation for antitumor agents targeted to a novel class of genetic structures able to regulate gene expression.
authors.affiliation: Laboratoire de Biophysique, Muséum National d'Histoire Naturelle, INSERM U 201 CNRS UA 481, Paris, France.
authors.forename: G
authors.initials: G
authors.lastname: Duval-Valentin
authors.forename: T
authors.initials: T
authors.lastname: de Bizemont
authors.forename: M
authors.initials: M
authors.lastname: Takasugi
authors.forename: J L
authors.initials: JL
authors.lastname: Mergny
authors.forename: E
authors.initials: E
authors.lastname: Bisagni
authors.forename: C
authors.initials: C
authors.lastname: Hélène
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000138:chemical synthesis / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects*; D004259:DNA-Directed DNA Polymerase / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004720:Endonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D006358:Hot Temperature; D007211:Indoles / Q000494:pharmacology*; D007364:Intercalating Agents / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D011725:Pyridines / Q000494:pharmacology*; D014158:Transcription, Genetic; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D007211:Indoles; D007364:Intercalating Agents; D011725:Pyridines; C051802:triplex DNA; C082732:3-methoxy-7H-8-methyl-11-((3'-amino)propylamino)benzo(e)pyrido(4,3-b)indole; D004247:DNA; D004259:DNA-Directed DNA Polymerase; D004720:Endonucleases; D001618:beta-Lactamases