The non-histone nuclear phosphoprotein B2 (Mr 68,000; pI 6.5-8.2) was found to bind specifically defined fragments of DNA. With the use of monoclonal IgG2A antibodies prepared against this nuclear antigen, nucleosomal DNA fragments associated with phosphoprotein B2 were isolated and cloned. Nine cloned fragments were sequenced and analysed for similarity. The clone having the most similarity to the others was chosen to serve as a model in gel shift and footprinting assays. Subsequently, the DNA binding site was found to reside within a 30 bp region. Synthetic oligonucleotides corresponding to this site confirmed the specificity of DNA binding exhibited by the nuclear antigen as demonstrated in competition assays. Moreover, a 5′-TATTAG/C-3′ motif was found to exist within the binding site and in the other sequenced clones, possibly implicating the involvement of this motif in protein binding.
