Viral Enzymes

[SysBio]

(I posted this in the Cell Biology forum but did not get a response, so I am re-posting this here )

For the viruses that must carry a specific enzyme (eg. viruses with ssDNA, -ssRNA genomes):

1. It is carried in the capsid AND coded for in their genomes, right?

2. since they need this enzyme before they can use their genome, how do they ensure that a lot is transcribed?

Thanks in advance...

[biohazard]

Umm, not sure I got your question right, but viruses use the host cell's synthesis machinery to produce all the enzymes they need, including the ones that are required for the conversion of their genome (e.g. reverse transcriptase for RNA viruses). These are then packed into the viral particle during the viral assembly.

So, because they already carry the enzyme within the capsid, it is ready to use when the virus offloads its "cargo" into their target cell. In the cell, all parts of the virus are then produced again and assembled into a functional virus, including fresh copies of the enzyme(s) they need.

Naturally many viral particles are produced that are inactive because the assembly has failed, for example if some of the required enzymes did not get loaded into the capsid. Depending of the virus type, inactive viruses may constitute several percents of the total number of viral particles.