title: Chromium(III) bound to DNA templates promotes increased polymerase processivity and decreased fidelity during replication in vitro.
abstract: Carcinogenic chromium [Cr(VI)] compounds are reduced intracellularly to DNA- and protein-reactive chromium(III) species. However, the role of Cr(III) ions in chromium-induced genotoxicity remains unclear. We have investigated the effects of chromium(III) binding on DNA replication and polymerase processivity in vitro. Chromium ions bind slowly and in a dose-dependent manner to DNA. Micromolar concentrations of free chromium inhibit DNA replication, but if the unbound chromium is removed by gel filtration, the rate of DNA replication by polymerase I (Klenow fragment) on the chromium-bound template is increased greater than 6-fold relative to the control. This increase is paralleled by as much as a 4-fold increase in processivity and a 2-fold decrease in replication fidelity. These effects are optimum when very low concentrations of chromium ions are bound to the DNA [3-4 Cr(III) ions per 1000 nucleotide phosphates]. Increased concentrations of chromium lead to the production of DNA-DNA cross-links and inhibition of polymerase activity. These results suggest that low levels of DNA-bound chromium(III) ions may contribute to chromium mutagenesis and carcinogenesis by altering the kinetics and fidelity of DNA replication.
authors.affiliation: Institute of Environmental Medicine, New York University Medical Center, Tuxedo 10987.
authors.forename: E T
authors.initials: ET
authors.lastname: Snow
authors.forename: L S
authors.initials: LS
authors.lastname: Xu
mesh_terms: D001665:Binding Sites; D002712:Chlorides; D002857:Chromium / Q000378:metabolism / Q000494:pharmacology*; D017608:Chromium Compounds; D004261:DNA Replication / Q000187:drug effects; D004277:DNA, Single-Stranded / Q000187:drug effects* / Q000378:metabolism; D004279:DNA, Viral / Q000187:drug effects / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D007700:Kinetics; D016296:Mutagenesis; D009691:Nucleic Acid Denaturation; D013698:Templates, Genetic
chemical_list: D002712:Chlorides; D017608:Chromium Compounds; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D002857:Chromium; C017133:chromous chloride; D004259:DNA-Directed DNA Polymerase