THE V(D)J RECOMBINATION SIGNAL SEQUENCE AND KAPPA-B BINDING-PROTEIN RC BINDS DNA AS DIMERS AND FORMS MULTIMERIC STRUCTURES WITH ITS DNA LIGANDS

The murine DNA binding protein Rc binds to the heptamer motif of the V (D)J recombination signal sequences and to the kappa B motif of the im munoglobulin enhancer. Bacterial fusion proteins for Rc and DNA ligand s of Rc form multiple protein - DNA complexes in electrophoretic mobil ity shift assays (EMSA). Large complexes formation is favored by an in creased Rc concentration. In order to determine the architecture of th ese complexes, the apparent molecular weights of the protein - DNA com plexes were first determined by their gel mobilities. The data suggest that Rc binds to its DNA ligands as dimers, tetramers, and multiples of tetramers. The inference that Rc binds DNA as dimers was substantia ted by the formation of chimeric complexes when two electrophoreticall y distinguishable Rc proteins were employed in EMSA. Methylation inter ference experiments show that there are no contiguous protein binding sites evident in the DNA of the larger complexes. Apparently, multimer ization occurs via protein-protein interactions. Such interaction was demonstrated by the formation of Rc dimers and tetramers in a chemical crosslinking experiment. Significantly, the multimerization of DNA-bo und Re could be involved in bringing the variable region gene segments together for the somatic V(D)J recombination.