Slipped (CTG)·(CAG) Repeats of the Myotonic Dystrophy Locus: Surface Probing with Anti-DNA Antibodies

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