DNA COMPRESSION CAUSED BY AN UPSTREAM POINT MUTATION

We observed an apparent series of insertions and deletions beginning 5 bp downstream of an A --> G silent transition in exon 1 of the tumor necrosis factor receptor 1 gene. The apparent sequence anomaly was obs erved only in individuals carrying the transition. Formamide gel elect rophoresis revealed that the apparent sequence anomaly was due to comp ression. The compression is plausibly explained by a hairpin in the re action products in a region of trinucleotide CAG repeats. One should s uspect the presence of DNA compression when a series of deletions and insertions follows a single base pair mutation that leads to a series of trinucleotide repeats.