Two auxiliary elements, Aux4 and Aux-2, contain binding sites for both T antigen and another
transcription factor, Spl (Kelly, 1988). The auxiliary sequences stimulate the T antigen-dependent DNA unwinding possibly by the interaction between proteins bound to these
sequences and T antigen (Guo et al.. 1989; Guo et al., 1991; Guo and DePamphiIis.
1992).