XRCC4 is a generally expressed protein of 334 amino acids that is invo
lved in the repair of DNA double-strand breaks and in V(D)J recombinat
ion, but its function is unknown. In this study, we have used a mutati
onal approach and the yeast two-hybrid method to perform an initial ch
aracterization of this protein, We show that the XRCC4 protein is loca
ted in the nucleus, We also demonstrate that several potential phospho
rylation sites are not required for XRCC4 function in a transient V(D)
J recombination assay, In addition, we show that XRCC4 forms a homodim
er in vivo with the homodimerization domain being located within amino
acids 115-204. Finally, we define a core domain of XRCC4 that functio
ns in V(D)J recombination and comprises amino acids 18-204, Potential
functions of XRCC4 are discussed.