Do some viruses that replicate in the cytoplasm contain RNA polymerases in their virions?

Question

As emerges from this previous Stack Exchange question and its answer, viruses in the family poxviridae have the potential to replicate in the cytoplasm because they encode their own DNA polymerases and RNA polymerases.

However, it seems to me that there's a bit of a the-chicken-and-the-egg problem here: DNA viruses needs RNA polymerase to make the mRNA encoding their proteins (including RNA polymerase), but they can't make these proteins without RNA polymerase to transcribe their DNA first!

Viruses that replicate inside the cell nucleus clearly don't run into this problem as they can use the host RNA polymerase already there. But how do viruses that replicate in the cytoplasm solve this conundrum? Do they carry sufficient RNA polymerase in their virions when the enter the cells or is there some other explanation?

Answer 1

Let us consider some different classes of viruses.

DNA viruses that do not encode their own DNA-dependent RNA polymerase replicate in the nucleus and so are able to utilize the host enzyme (and the DNA-dependent DNA polymerase). So there is no problem regarding production of RNA polymerase in this case.

The (double-stranded DNA) pox viruses, which do encode both their own DNA-dependent DNA polymerases and RNA polymerases, are unusual in that they replicate in the cytoplasm of the host. As the question states, in this case there is a problem of transcribing the viral genes encoding the DNA-dependent RNA polymerase that performs this transcription. As is explained in, e.g. this review by Bernard Moss not only the RNA polymerase, but approximately 20 other proteins devoted to synthesis and modification of mRNA. I reproduce part of Fig. 1 of that review below.

In positive-stranded RNA viruses the viral genome generally acts as mRNA, which can be translated into proteins (including the RNA-depenedent RNA polymerase — replicase — required for replication) by cytoplasmic ribosomes.

For negative-strand RNA viruses, the negative strand must be first replicated to produce a positive RNA strand (acting as mRNA) before synthesis of the RNA-dependent RNA polymerase can occur. As this requires viral RNA-dependent RNA polymerase, the circular problem of the source of the enzyme also arises in this case. As explained in an article by S. Payne, such viruses also carry the enzyme within their virion.