V(D)J RECOMBINATION INTERMEDIATES AND NONSTANDARD PRODUCTS IN XRCC4-DEFICIENT CELLS

V(D)J recombination assembles immunoglobulin (Ig) and T cell receptor (TCR) gene segments during lymphocyte development. Recombination is in itiated by the RAG-1 and RAG-P proteins, which introduce double-strand ed DNA breaks (DSB) adjacent to the Ig and TCR gene segments. The brok en ends are joined by the DSB repair machinery, which includes the XRC C4 protein, While XRCC4 is essential for both DSB repair and V(D)J rec ombination, the functions of this protein remain enigmatic. Because th e rare V(D)J recombination products isolated from XRCC4-deficient cell s generally show evidence of excessive nucleotide loss, it was hypothe sized that XRCC4 may function to protect broken DNA ends. Here we repo rt the first examination of V(D)J recombination intermediates in XRCC4 -deficient cells. We found that both types of intermediates, signal en ds and coding ends, are abundant in the absence of XRCC4, Furthermore, the signal ends are full length, We also showed that alternative V(D) J recombination products, hybrid joints, form with normal efficiency a nd without excessive deletion in XRCC4-deficient cells. These data ind icate that impaired formation of V(D)J recombination products in XRCC4 -deficient cells does not result from excessive degradation of recombi nation intermediates. Potential roles of XRCC4 in the joining reaction are discussed.