Final answer:
RNA-dependent RNA polymerase is the enzyme used by RNA viruses to replicate their RNA genome directly. Retroviruses like HIV use reverse transcriptase to convert RNA into DNA, but this is not for direct RNA replication.
Step-by-step explanation:
The enzyme used by RNA viruses to directly replicate the viral RNA genome is RNA-dependent RNA polymerase. This enzyme allows RNA viruses to use their RNA core as a template for the synthesis of viral genomic RNA and mRNA. RNA viruses typically encode their own RNA polymerase because host cells do not usually provide the necessary enzymes for RNA replication.
Retroviruses, like HIV, are an exception; they use reverse transcriptase to convert their RNA genome into DNA, which can be integrated into the host cell genome. However, for direct RNA to RNA replication, RNA-dependent RNA polymerase is used, not reverse transcriptase.