Sequence analysis of genomic regions containing trinucleotide repeats isolated by a novel cloning method

A method was developed for effective isolation of trinucleotide repeats from genomic DNA. This method is based on the DNA polymerase reaction, which is restricted with only two or three nucleotide substrates and primed by biotinylated oligonucleotide probes. Sequences are then isolated by a streptavidin biotin-trapping method. More than 80% of the clones from each library contained more than eight trinucleotide repeats. Sequence analysis showed that the characteristic dinucleotide flanking sequences usually confronting various trinucleotide repeats are not found in the vicinity of CAG repeats, suggesting that CAG repeats may have been generated through a mechanism different from that of other trinucleotide repeats.