Replication of the linear genome of Parvoviridae (eg. feline parvovirus; human parvovirus B19) involves use of a semi-stable genomic 3'-hairpin structure as a primer, synthesis of new DNA by host delta DNA pol using genomic DNA as template, covalent closure then re-opening of the circular DNA product, and re-initiation at the new 3'-terminus as primer after transient hairpin formation at the new 3' end after "melting" of the newly-formed duplex. A complicated series of steps follows, involving repeated single-strand cleavages and 5'-end binding by virus-coded NS1 protein, and possible topoisomerase action.
The other circular genomes can replicate by a "rolling circle" model: nicking of one strand of the cccDNA RF allows use of an exposed 3'-terminus as a primer, which results in elongation of the "primer" strand, and displacement of the other. Ordinarily this results in greater-than- unit-length ss- and dsDNA forms being found in infected cells.
