ISOLATION OF ACTIVE GENES CONTAINING CAG REPEATS BY DNA STRAND INVASION BY A PEPTIDE NUCLEIC-ACID

An amplification of tandem CAG trinucleotide sequences in DNA due to e rrors in DNA replication is involved in at least four hereditary neuro degenerative diseases, The CAG triplet repeats when translated into pr otein give rise to tracts of glutamine residues, which are a prominent feature of many transcription factors, including the TATA-binding pro tein of transcription factor TFIID. We have used a biotin-labeled, com plementary peptide nucleic acid (PNA) to invade the CAG repeats in int act chromatin and then employed a method For the selective isolation o f transcriptionally active chromatin restriction fragments containing the PNA . DNA hybrids. The PNA-containing chromatin fragments were cap tured on streptavidin-agarose magnetic beads and shown to contain all the CAG . PNA hybrids of the active chromatin fraction. DNA hybridizat ion experiments using a DNA probe specific for unique sequences downst ream of the CAG-tandem repeats confirmed that the PNA . DNA hybrids co ntained the transcribed gene for the TATA-binding protein. In contrast , no hybridization signal was detected with a DNA probe specific for t he c-myc protooncogene, which is amplified and transcriptionally activ e in COLO 320DM cells but lacks CAG tandem repeats.