The immunoglobulin (Ig) and T cell receptor (TCR) 1 genes are assembled by a complex process of V(D)J recombination to generate antigen receptor diversity. In this process, the antigen binding domains of Ig and TCR chains that are encoded by germline variable (V), diversity (D), and joining (J) gene segments are rearranged to produce functional B or T cell receptors (1-3). For IgH and TCR chains, V, D, and J gene segments are involved whereas for IgL and TCR␣ chains, V and J gene segments take part in the recombination event (4 -6). V(D)J recombination is known to be stage-specific within a given lymphoid lineage, and the antigen receptors are expressed from only one of the two alleles; the phenomenon called allelic exclusion (7,8). At the TCR locus, the recombination occurs during DN (CD4 Ϫ CD8 Ϫ CD44 Ϫ CD25 ϩ ) stage of thymocyte development (9). V(D)J recombination is mediated by lymphoid and non-lymphoid-specific factors as well as cis regulatory elements (10). The lymphoid-specific factors of the recombination machinery include recombination activating genes (RAG) 1 and 2, and terminal deoxynucleotidyltransferase (TdT) (6, 10, and 11). Besides lymphoid-specific factors, nonlymphoid-restricted factors have also been implicated in the regulation of the recombination process. Among these, proteins that are involved in DNA double-strand break repair also play a critical role in the recombination events. These include Ku-80, XRCC4 protein, the catalytic subunit of DNA-dependent protein kinase (DNA-PK), and poly(ADP-ribose) polymerase (PARP) (12)(13)(14).