Expanded CGG repeats cause chromosomal fragility and hereditary neurological disorders in humans. These repeats adopt unusual structures that block DNA replication in vitro and in unicellular organisms. Mirkin and co-workers asked whether the same holds true in mammalian cells. They find that CGG repeats stall replication forks in a length-dependent, but orientation-independent, manner and do not seem to trigger an intra–S phase checkpoint response. They suggest that fragile sites arise because the cell cycle continues before replication is complete and the under-replicated areas would convert into constrictions and/or double-stranded breaks.
- Irina Voineagu
- Christine F Surka
- Sergei M Mirkin
