The locus of Epstein-Barr virus terminal repeat processing is bound with enhanced affinity by Sp1 and Sp3.
EBV DNA contains G-rich, repeat regions that are involved in rearrangement and recombination events including terminal repeat (TR) processing and the EBNA-2 deletion in the EBV strain P3HR-1. Cellular proteins, called terminal or tandem repeat binding proteins (TRBPs), recognize sequences at the junctions of these recombination events. In this study, using antibody supershift assays and expression of recombinant proteins, we show that Sp1 and Sp3 are the sequence-specific components of TRBP and that Ku is the nonspecific binding component. Sp1 binds other recombinogenic regions of EBV DNA, but Sp3 does not bind to the large internal repeat. The sequence GGGGTGGGG, a low affinity site for Sp1 and Sp3, is the minimal binding site within terminal repeat binding site 1 (TRBS1). However, 3' flanking sequences in the sequence GGGGTGGGGCATGGGG augment binding of Sp1 and Sp3 so that their affinity of binding is increased approximately twofold relative to a classical high-affinity Sp1 site. EBV lytic cycle induction does not alter the abundance or binding activity of any of the three identified components of TRBP. Sp1 and Sp3 may act in trans to promote EBV terminal repeat processing and possibly other viral and cellular recombination events.