below are hereby incorporated by reference the following methods were utilized to realize the use of the invention additional materials and methods are described in co owned u s ser no 632 027 filed dec 21 1990 the conditions for bpv replication in vitro were derived from li and kelly 21 with some modifications extracts from the mouse fm3a cell line were prepared as follows cells were grown in a 2 liter suspension culture containing rpmi 1640 media supplemented with 25 mm hepes ph 7 2 and 5 calf serum the cells were harvested at a density of 7 u00d7 10 5 cells ml the cell pellet was washed with 30 mls of cold pbs and then 10 mls of hypotonic buffer 20 mm hepes ph 7 5 5 mm kcl 1 mm edta 0 5 mm dtt the cells were then resuspended in hypotonic buffer to a final volume of 10 mls and incubated on ice for 15 min after 20 strokes in a dounce homogenizer with b pestol 500 u03bcl of 5m nacl was added and the extraction mixture was incubated on ice for 30 60 min this mixture was centrifuged in an sw41 rotor at 20k rpm for 30 min and the supernatant was dialyzed twice against 1 liter d buffer 20 mm hepes ph 7 5 10 mm nacl 1 mm edta and 0 5 mm dtt the extract was then centrifuge in.