BIOCHEMICAL AND IMMUNOLOGICAL CHARACTERIZATION OF THE DNA-BINDING PROTEIN (RBP-J-KAPPA) TO MOUSE J-KAPPA RECOMBINATION SIGNAL SEQUENCE

We have investigated whether J(kappa) recombination signal sequence (RS) binding protein (RBP-J(kappa)) has any partial catalytic activities involved in the VDJ recombination reaction, such as cleavage, ligation, and bending of DNA. Murine RBP-J(kappa) protein purified by J(kappa)-RS affinity chromatography did not show DNA cleavage activities but contained a strong DNA ligase activity. To obtain a large amount of purified RBP-J(kappa)protein, recombinant RBP-J(kappa) was synthesized in Escherichia coli as a fusion protein and also in silkworm cells. Although recombinant RBP-J(kappa) produced in silkworm cells could bind J-kappa(RS), it failed to show either ligase or DNA bending activity. Since the DNA affinity-purified RBP-J(kappa) has the ligase activity, the RBP-J(kappa) protein may form a complex with a ligase in vivo. We have raised monoclonal antibodies against the RBP-J(kappa) fusion protein which was synthesized in E. coli and unable to bind J(kappa)-RS. Using the anti-RBP-J(kappa) monoclonal antibody we have shown that the RBP-J(kappa) protein is expressed ubiquitously in mammalian tissues. The ubiquitous expression of the RBP-J(kappa) protein is consistent with the hypothesis that the RBP-J(kappa) protein may have dual function [Furukawa et al. (1991) J. Biol. Chem. 266, 23334-23340].