Rolling circular DNA associated with Dane particles in hepatitis B virus

Abstract

PLASMA of hepatitis B antigen (HB_sAg) carriers consists mostly of spherical particles of diameter 20 nm, together with a much smaller number of filamentous structures with the same diameter. In addition, larger spherical particles, 42 nm in diameter with a 28 nm core, first described by Dane et al.¹, are routinely found in crude plasma or purified preparations of HB_sAg. Dane particles also contain a primed DNA polymerase activity² capable,of synthesising new DNA. Robinson et al.² examined DNA from Dane particles by electron microscopy and found open, double-stranded circular configurations approximately 0.78 µm long. We have examined DNA isolated from Dane particles directly and also after formation of radioactive products by the endogenous DNA polymerase reaction. The DNA structures appeared in electron micrographs as double-stranded linear strands and closed circles, with examples of completely and partially open circles, and circles with attached linear segments in different lengths. The open circles with attached linear segments are suggestive of a replicative form, and this is consistent with a rolling circle model⁴ for replication. This model for replication is strengthened by the comparison of the types of DNA found in particles before and after reaction of the polymerase. The number of rolling circles and the length of the tails were greatly increased after DNA synthesis. This type of replication has not been reported for animal viruses.