The telomere is a functional domain of the chromosome, located at the extreme ends, and is essential for normal chromosome stability. Chromosomes lacking telomeres are inherited improperly, and mutations in the telomeric repeat sequences are thought to lead to senescence and possibly to cancer. The molecular mechanisms maintaining chromosomes by telomeres, however, have been unclear. Results recently reported by Kirk et al.(1) offer an insight into new telomerase function. They have identified a novel telomerase mutation that blocks sister chromatid separation (...) in mitosis. (shrink)