HCK 18:1Bj and HCK 18:1Bs formed readily observable bands
at the expected density following isopycnic gradient centrifugation
(Fig. 3). Gradient fractions were collected and analyzed
by Southern blot hybridization, confirming the presence of
HPV18 DNA (Fig. 4). Gradient fractions 7, 8, and 9 were
found to contain HPV18 DNA at high levels (Fig. 4). Fractions
positive for HPV18 DNA correlated with fractions where the
banded virus was observed in the gradient (Fig. 3 and 4) and
had the buoyant density reported for papillomaviruses (29).
Gradient fractions positive for HPV18 DNA were investigated
for the presence of viral particles. As demonstrated by
electron microscopy, both the parental HCK 18:1B cell line
(Fig. 5D) and the subcloned HCK 18:1Bj and HCK 18:1Bs cell
lines (Fig. 5A to C, E, and F) were able to support the production
of HPV18 virions, albeit in vastly different quantities.
Data from Southern blot hybridization analysis indicated