Repair of DNA double-strand breaks and homologous recombination

This chapter examines the repair of DNA double-strand breaks and homologous recombination. DNA double-strand breaks are particularly dangerous lesions—failure to repair them can lead to chromosome fragmentation and cell death. There are two major strategies for double-strand break repair: non-homologous end joining (NHEJ) and homology-directed repair. NHEJ rejoins the ends across a double-strand break in the absence of a DNA template. It is often mutagenic because of nucleolytic processing of the ends prior to joining. Meanwhile, homology-directed DNA synthesis can repair double-strand breaks by synthesizing new DNA across the break. The chapter then explains homologous recombination, which is the reciprocal exchange of large segments of DNA between homologous duplexes. Homologous recombination occurs during meiosis to generate gametes and occurs between the bacterial chromosome and exogenous DNA that enter the cell by conjugation or transformation, or in viruses.