Researchers have long known that some repetitive DNA sequences can make human chromosomes "fragile," i.e. appearing constricted or even broken during cell divisions.
Scientists at Tufts University have found that one such DNA repeat not only stalls the cell's replication process but also thwarts the cell's capacity to repair and restart it. The researchers focused on this CGG repeat because it is associated with hereditary neurological disorders such as fragile X syndrome and FRAXE mental impairment.
In a study to be published in the January 2009 issue of the journal Nature Structural and Molecular Biology , Sergei Mirkin, White Family Professor of Biology at Tufts' School of Arts and Sciences, along with graduate students Irina Voineagu and Christine F. Surka and postdoctoral fellows Alexander A. Shishkin and Maria M. Krasilnikova, explored the link between CGG repeats and replication delays. Mirkin's research was funded by the National Institutes of Health.
Effect of palindromes
Past research from Mirkin's lab had shown that peculiar long DNA sequences named palindromes change the shape of the molecule from a double helix into a hairpin-like structure and, as a result, stall replication. When this happens chromosomes can break during cell division.