Question

Why must some viruses enter the nucleus to replicate whereas others do not?

Answer 1

The virus which has RNA in their genome replicate in the cytoplasm becuase they have their own RNA polymerase which helps in replication of RNA. The other reason is that the splicing enzymes can modify their RNA as they get to the nucleus.

While the DNA viruses replicate mostly in the nucleus as they dont have DNA and RNA polymerase for replication and transcription so they have to get into the nucleus where they use the host RNA and DNA polymerase for transcription. That is why they have to go into the nucleus to get replicated.