The DNA-binding ability of HIVEP3/KRC decreases upon activation of V(D)J recombination

Abstract.

Somatic V(D)J recombination of the immune receptor genes is mediated by the recombination signal sequence (RSS) and the recombination-activating genes RAG1 and RAG2. Previously, proteins binding specifically to the RSS have been characterized in nuclear extracts of T and B lymphocytes. Further elucidation of the role of those RSS-binding proteins in V(D)J recombination, however, has been hampered by the fact that their identities have not been established. Here, we show that the major RSS-binding protein present in the nuclear extracts of B lymphocytes is an M _r  135,000 species. Notably, its affinity for the RSS decreased when RAG1 and RAG2 were induced. In immunoblot analyses and gel supershift assays, we showed that KRC antisera react with the M _r  135,000 RSS-binding protein. We previously cloned KRC from a thymocyte expression library using ³²P-RSS as a ligand and showed that KRC fusion proteins bind specifically to the RSS and to the κB enhancer motif. The lymphoid expression and DNA-binding characteristics suggest that KRC may be involved in lymphocyte development.