title: The SV40 large T-antigen helicase can unwind four stranded DNA structures linked by G-quartets.
abstract: We describe a novel activity of the SV40 large T-ag helicase, the unwinding of four stranded DNA structures linked by stacked G-quartets, namely stacked groups of four guanine bases bound by Hoogsteen hydrogen bonds. The structures unwound by the helicase were of two types: (i) quadruplexes comprising four parallel strands that were generated by annealing oligonucleotides including clustered G residues in a buffer containing Na+ions. Each parallel quadruplex consisted of four oligonucleotide molecules. (ii) Complexes comprising two parallel and two antiparallel strands that were generated by annealing the above oligonucleotides in a buffer containing K+ions. Each antiparallel complex consisted of two folded oligonucleotide molecules. Unwinding of these unusual DNA structures by the T-ag was monitored by gel electrophoresis. The unwinding process required ATP and at least one single stranded 3'-tail extending beyond the four stranded region. These data indicated that the T-ag first binds the 3'-tail and moves in a 3'-->5'direction, using energy provided by ATP hydrolysis; then it unwinds the four stranded DNA into single strands. This helicase activity may affect processes such as recombination and telomere extension, in which four stranded DNA could play a role.
authors.affiliation: Department of Biology, Technion-Israel Institute of Technology, Haifa 32,000, Israel.
authors.forename: N
authors.initials: N
authors.lastname: Baran
authors.forename: L
authors.initials: L
authors.lastname: Pucshansky
authors.forename: Y
authors.initials: Y
authors.lastname: Marco
authors.forename: S
authors.initials: S
authors.lastname: Benjamin
authors.forename: H
authors.initials: H
authors.lastname: Manor
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D018983:DNA Footprinting; D004265:DNA Helicases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006860:Hydrogen Bonding; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism; D013539:Simian virus 40 / Q000201:enzymology*; D013696:Temperature
chemical_list: D000952:Antigens, Polyomavirus Transforming; D009838:Oligodeoxyribonucleotides; D000255:Adenosine Triphosphate; D004247:DNA; D004265:DNA Helicases