Final answer:
Class IV viruses use their own RNA-dependent RNA polymerase to replicate their genome within the host cell, as this enzyme is not found in typical host cells and is necessary for RNA to RNA replication.
Step-by-step explanation:
The replication mechanism of a virus depends on its genome type. Class IV viruses belong to the Baltimore classification and are characterized as positive-sense single-stranded RNA viruses (ssRNA).
These viruses require RNA-dependent RNA polymerase to replicate their genomes because this enzyme uses RNA as a template to synthesize new RNA strands. Since host cells typically do not have this enzyme, class IV viruses must encode their own RNA-dependent RNA polymerase. Hence, when a class IV virus infects a host cell, it uses its own RNA-dependent RNA polymerase to replicate its genome.