Purification and characterization of a protein that binds to the recombination signal sequence of the immunoglobulin Jxsegment

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Abstract
A protein that binds to the recombination signal sequence (RS) of the immunoglobulin Jx segment was purified almost to homogeneity from the nuclear extract of a murine pre-B cell line 38B9. A similar binding protein was found in lymphoid cell lines but not in non-lyrnphoid cell lines. The binding activity was associated with a polypeptide with a molecular weight of 60,000. DNase I footprinting analysis demonstrated that this binding protein interacted with the heptamer and several 3′ bases close to the heptamer. The Kd value of the Jx RS binding protein to the Jx RS was 1 nM. One base substitution in the heptamer of the Jx RS greatly reduced the affinity of the Jx RS binding protein. The high specificity of the binding site of the Jx RS binding protein suggests that this protein may be involved in V-J recombination.