Persistent infection by papillomaviruses involves the maintenance of
viral DNA as a nuclear plasmid, the replication of which requires host
DNA polymerases. The role of the cellular
DNA polymerase alpha-primase holoenzyme was probed by using soluble extracts from rodent cells that replicate bovine
papilloma virus 1 and human papilloma virus 6b
DNA in the presence of the viral E1 helicase and the E2
transcription factor.
Monoclonal antibodies directed against the catalytic 180-kDa subunit of polymerase alpha inhibit
DNA synthesis in this system. Addition of purified human polymerase alpha-
primase holoenzyme to neutralized extracts restores their
DNA synthetic activity. The amino-terminal 424
amino acids of E1 forms a specific
protein complex with the p180 polymerase subunit.
Immune complexes can be isolated with
antibodies directed against E1 that contain
a DNA polymerase activity. Moreover, this polymerase activity can be neutralized by anti-polymerase alpha
antibodies. Permissivity barriers were not encountered in this in vitro system, as bovine E1 can interface with the murine and human replication apparatus. Although the large
tumor antigens encoded by simian virus 40 and polyoma share limited primary sequence homology with the papillomavirus E1
proteins, the organization of functional motifs at the level of primary protein structure is remarkably similar. In addition to their origin-specific
DNA-binding activity, each of these helicases may function to help recruit the cellular polymerase alpha-
primase complex to the viral replication origin.