Abstract
V:(D)J recombinationis initiated by the synapsis and cleavage of a complementary(12123) pair of recombination signalsequences (RSSs) by the RAG1 and RAG2 proteins. Our understanding of these processes has been greadyaided by the development of in vitro biochemicalassays of RAG binding and cleavage activity. Accumulating evidencesuggests that synapticcomplexassembly occursin a step-wise manner and that the RAG proteins catalyze RSS cleavage by mechanisms similar to those used by bacterial transposases. In this chapter we will reviewthe molecularmechanisms of RAG synapticcomplexassembly and 12123-regulated RSS cleavage, focusingon recent advances that shed newlight on theseprocesses.