Use of Gene Targeting to Study Recombination in Mammalian DNA Repair Mutants

Gene targeting, defined as homologous recombination or genetic exchange between an introduced DNA sequence and its endogenous chromosomal locus, or “target,” is a powerful approach for genetic manipulation. Gene-targeting strategies for both yeast (1 ) and mammalian cells (2 –4 ) have been described that allow correction, disruption, deletion, replacement, or site-directed modification of virtually any gene or chromosomal locus for which a cloned sequence is available. The majority of mammalian gene-targeting studies have been directed toward disruption (“knockout”) of a selected target gene locus in mouse embryo stem (ES) cells (4 ,5 ), with the primary objective of obtaining the desired mutant mouse as quickly as possible. Relatively few studies have examined targeted recombination in cell types other than mouse ES cells. This chapter describes methods and use of targeted recombination as an approach to study mechanisms of recombination in cultured mammalian cells, and, in particular, the use of gene-targeting approaches to generate and analyze DNA repair-deficient knockout mutants to reveal interactions between DNA repair and recombinational pathways in mammalian cells.