E1 PROTEIN OF HUMAN PAPILLOMAVIRUS TYPE 1A IS SUFFICIENT FOR INITIATION OF VIRAL-DNA REPLICATION

Previous studies on transient replication of papillomaviruses have sho wn an absolute requirement for the viral E1 and E2 proteins in DNA rep lication. Here we demonstrate that for human papillomavirus type 1a (H PV-1a) DNA, the E1 protein alone is sufficient for in vivo replication of plasmids containing the viral origin of replication. Replication w as origin-specific and required the presence of a DNA sequence contain ing a putative E1 binding site, but the E2 binding sites were dispensa ble. In the presence of the E1 protein, E2 stimulated replication of p lasmids containing the E1 and E2 binding sites, but no stimulation was observed when the origin plasmids lacked E2 binding sites. Conversely , in the presence of E1 alone, the E2 binding sites did not affect rep lication. Plasmids containing the replication origins of HPV-6b, HPV-1 8, and bovine papillomavirus type 1 (BPV-1) also replicated efficientl y in the presence of the HPV-1a E1 and E2 proteins. However, plasmids containing the origins of HPV-6b and HPV-18 failed to replicate in the presence of HPV-1a E1 alone, whereas a plasmid containing the BPV-1 o rigin replicated to lower levels than the HPV-1a origin-containing pla smid. These results suggest that replication from papillomaviral origi n's in the presence of E1 alone is presumably dependent on the strengt h of E1-origin interactions. Additionally, E1-dependent replication is stimulated by the E2 protein in the presence of E2 binding sites.