Question

What is the typical reproduction cycle of a DNA virus?

Answer 1

The single stranded DNA genome is initially converted to double-stranded DNA by host cell enzymes and then is inverted terminal repeat (ITR) sequences at the each extremity of the viral genome fold back on themselves, so that the free 3' OH group at the end of the virus single-stranded genome can be used as a primer for the synthesis of the complementary DNA strand on the whole.

The double-stranded parvovirus B-19 genome has a single promoter element and this enables in recruiting the cellular transcription factors and RNA polymerase. Alternative splicing generates mRNAs coding for the two capsid proteins (VP1 and VP2) and the non-structural protein NS1. These viral proteins are all synthesized in the cytoplasm, then imported into the nucleus.

NS1 is highly essential for replication of the virus genome – but it is not a DNA polymerase. Instead, NS1 acts as an origin recognition protein, which specifically binds to double-stranded virus DNA and allows host DNA polymerase to replicate viral DNA, generating many single-stranded copies of the parvovirus genome. Parvovirus B19 can only replicate in actively cycling cells, that express all of the cellular factors necessary for DNA replication.

Both (+) and (-) strand copies are generated, and both can either be converted into double stranded genomes or converted to virions on the whole.