title: Slipped (CTG).(CAG) repeats of the myotonic dystrophy locus: surface probing with anti-DNA antibodies.
abstract: At least 15 human diseases have been associated with the length-dependent expansion of gene-specific (CTG).(CAG) repeats, including myotonic dystrophy (DM1) and spinocerebellar ataxia type 1 (SCA1). Repeat expansion is likely to involve unusual DNA structures. We have structurally characterized such DNA, with (CTG)(n).(CAG)(n) repeats of varying length (n=17-79), by high-resolution gel electrophoresis, and have probed their surfaces with anti-DNA antibodies of known specificities. We prepared homoduplex S-DNAs, which are (CTG)x.(CAG)y where x=y, and heteroduplex SI-DNAs, which are hybrids where x>y or x<y. S-DNAs formed many different species of slipped isomers, as indicated by its multiple electrophoretic species. In contrast, SI-DNAs formed distinct structures, as indicated by the limited electrophoretic species for all possible repeat length pairings. Sister SI-DNAs with an excess of CAG repeats always migrated slower than their sister SI-DNAs with an excess of CTG repeats. Strikingly, both the propensity to form slipped structures and the pattern of S-DNAs, but not SI-DNAs, varied for similar lengths of CTG/CAG repeats between the DM1 and SCA1 loci, highlighting a role for flanking cis-elements in S-DNA but not SI-DNA formation. Slipped structures bound structure and nucleotide-specific anti-DNA antibodies. Binding of anti-B-DNA antibodies was reduced for both S-DNAs and SI-DNAs relative to their linear forms. SI-DNAs bound anti-Z-DNA antibodies, while both S and SI-DNAs bound anti-cruciform antibodies, revealing shared characteristics between the corresponding DNA structures and slipped DNAs. Such features of the repeats may be recognized by cellular proteins known to bind such structures.
authors.affiliation: Program of Genetics and Genomic Biology, The Hospital for Sick Children, Room 11-135, 555 University Avenue, Elm Wing, M5G 1X8, Toronto, Ont., Canada
authors.forename: Mandy
authors.initials: M
authors.lastname: Tam
authors.forename: S
authors.initials: S
authors.lastname: Erin Montgomery
authors.forename: Mariana
authors.initials: M
authors.lastname: Kekis
authors.forename: B David
authors.initials: BD
authors.lastname: Stollar
authors.forename: Gerald B
authors.initials: GB
authors.lastname: Price
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Pearson
mesh_terms: D000974:Antibodies, Antinuclear / Q000378:metabolism*; D000918:Antibody Specificity; D000067696:Ataxin-1; D000067528:Ataxins; D020029:Base Pairing; D004247:DNA / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008274:Magnesium / Q000378:metabolism; D009223:Myotonic Dystrophy / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes; D009705:Nucleosides / Q000276:immunology; D013499:Surface Properties; D018911:Trinucleotide Repeats / Q000276:immunology*
chemical_list: C000593749:ATXN1 protein, human; D000974:Antibodies, Antinuclear; D000067696:Ataxin-1; D000067528:Ataxins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D009692:Nucleic Acid Heteroduplexes; D009705:Nucleosides; D004247:DNA; D008274:Magnesium