Induction of structural changes in the bovine papillomavirus type 1 origin of replication by the viral E1 and E2 proteins

Chemical and enzymatic probing techniques were used to examine the interaction of the bovine papilloma-virus type 1 E1 and E2 proteins with the viral origin of replication (ori). E1 was found to generate significant distortions to the structure of ori, as assayed by KMnO₄ oxidation of DNA. The primary site of ori distortion was located within and adjacent to the AT- element of the core replicator sequence, although a number of minor structural transitions were also detected. The induction of these structural changes required ATP and appeared to require ATP hydrolysis. E2 was found to decrease the amount of E1 required for ori distortion but did not significantly alter the pattern of structural distortion. In contrast, the presence of E2 resulted in a biphasic mechanism for E1 binding to ori, as assayed by nuclease protection. Under these conditions, E1 bound preferentially to the dyad symmetry region containing the conserved Hpa I site. Higher levels of El were required for binding to the adjacent ori AT- rich region. Thus, these data suggest that E2 can order the stepwise binding of E1 to ori.