title: Eukaryotic topoisomerase II cleavage of parallel stranded DNA tetraplexes.
abstract: A guanine-rich single-stranded DNA from the human immunoglobulin switch region was shown by Sen and Gilbert [Nature, (1988) 334, 364-366] to be able to self-associate to form a stable four-stranded parallel DNA structure. Topoisomerase II did not cleave the single-stranded DNA molecule. Surprisingly, the enzyme did cleave the same DNA sequence when it was annealed into the four-stranded structure. The two cleavage sites observed were the same as those found when this DNA molecule was paired with a complementary molecule to create a normal B-DNA duplex. These cleavages were shown to be protein-linked and reversible by the addition of salt, suggesting a normal topoisomerase II reaction mechanism. In addition, an eight-stranded DNA molecule created by the association of a complementary oligonucleotide with the four-stranded structure was also cleaved by topoisomerase II despite being resistant to restriction endonuclease digestion. These results suggest that a single strand of DNA may possess the sequence information to direct topoisomerase II to a binding site, but the site must be base paired in a proper manner to do so. This demonstration of the ability of a four-stranded DNA molecule to be a substrate for an enzyme further suggests that these DNA structures may be present in cells.
authors.affiliation: Department of Molecular Genetics, Ohio State University, Columbus 43210.
authors.forename: I K
authors.initials: IK
authors.lastname: Chung
authors.forename: V B
authors.initials: VB
authors.lastname: Mehta
authors.forename: J R
authors.initials: JR
authors.lastname: Spitzner
authors.forename: M T
authors.initials: MT
authors.lastname: Muller
mesh_terms: D000818:Animals; D001482:Base Composition / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002645:Chickens; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007134:Immunoglobulin Switch Region / Q000235:genetics*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data
chemical_list: D004277:DNA, Single-Stranded; D046911:Macromolecular Substances; D004250:DNA Topoisomerases, Type II