At the crossroads of chromosomes

PHILADELPHIA — On average, one hundred billion cells in the human body divide over the course of a day. Most of the time the body gets it right but sometimes, problems in cell replication can lead to abnormalities in chromosomes resulting in m…

Protective protein blocks DNA breaks at fragile sites

With 46 chromosomes and six feet of DNA to copy every time most human cells divide, it’s not surprising that gaps or breaks sometimes show up in the finished product – especially when the cell is under stress or dividing rapidly, as in cancer. But what is surprising is that the breaks don’t always occur at random. They happen at a few specific locations on chromosomes, when cells are under stress, during the stages in the cell cycle where DNA is copied, or replicated, and the cell splits into two identical daughter cells. Scientists call them fragile sites, but the reasons for their inherent instability have remained a mystery. Now researchers have discovered that a protein called ATR protects fragile sites from breaking during DNA replication.