The V(D)J recombination signal sequence and χB binding protein Rc binds DNA as dimers and forms multimeric structures with its DNA ligands

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Abstract
The murine DNA binding protein Re binds to the heptamer motif of the V(D)J recombination signal sequences and to the χB motif of the immunoglobulin enhancer. Bacterial fusion proteins for Rc and DNA ligands of Rc form multiple protein - DNA complexes in electrophoretlc mobility shift assays (EMSA). Large complexes formation is favored by an Increased Rc concentration. In order to determine the architecture of these complexes, the apparent molecular weights of the protein - DNA complexes were first determined by their gel mobilities. The data suggest that Rc binds to its DNA ligands as dlmers, tetramers, and multiples of tetramers. The Inference that Rc binds DNA as dimers was substantiated by the formation of chimerlc complexes when two electrophoretically distinguishable Rc proteins were employed in EMSA. Methylatlon interference experiments show that there are no contiguous protein binding sites evident in the DNA of the larger complexes. Apparently, multlmerlzation occurs via protein-protein interactions. Such interaction was demonstrated by the formation of Rc dlmers and tetramers In a chemical crosslinking experiment. Significantly, the multimerizatlon of DNA-bound Rc could be involved In bringing the variable region gene segments together for the somatic V(D)J recombination.