Repair of double-strand breaks As we have seen, DNA complementarity is an important resource that is exploited by many error-free correction systems. Such error-free repair is characterized by two stages: (1) removal of damaged and nearby DNA from one strand of the double helix and (2) use of the other strand as a template for the DNA synthesis needed to Fll the single-strand gap. However, what would happen if both strands of the double helix were damaged in such a way that complementarity could not be exploited? One way this might happen is if both strands of the double helix were to break at sites that were close together. A mutation like this is called a double-strand break. If left unrepaired, double-strand breaks can cause a variety of chromosomal aberrations resulting in cell death or a precancerous state. Interestingly, the ability of double-strand breaks to ini-tiate chromosomal instability is an integral feature of some normal cellular processes that require DNA rearrange-ments. One example is the generation of the diversity of antibodies in the cells of the mammalian immune system.
This is the end of the preview. Sign up
access the rest of the document.