CAG repeats in various organisms studied by Southern blot analysis

A 90-nucleotide (CAG)30, single-stranded DNA was used to probe Southern blots in order to indicate the quantity and distribution of long CAG repeats in selected genomes. Bovine and rat genomes were found to contain a particularly high content of CAG repeats, while the repeats were comparatively rare in the human genome. A particularly strong signal in the bovine genome was due to a CAG repeat associated with the 1.709 satellite. A similar element was found in goat and musk, but not in the other artiodactyls tested, suggesting that this particular CAG repeat developed some 10-20 million years ago within a 3.8-kb unit presently belonging to the satellite element and that this unit has later multiplied in the genome. Single-copy repeats could be discerned in yeast, but not in mammals. Thus the probe did not detect specific repeats in patients with CAG repeat diseases.