Editing RNA virus (section)

==Replication==
There are three distinct groups of RNA viruses depending on their genome and mode of replication:
* Double-stranded RNA viruses (Group III) contain from one to a dozen different RNA molecules, each coding for one or more viral proteins.
* Positive-sense ssRNA viruses (Group IV) have their genome directly utilized as mRNA, with host [[ribosomes]] [[Translation (biology)|translating]] it into a single protein that is modified by host and viral proteins to form the various proteins needed for replication. One of these includes RNA-dependent RNA polymerase (RNA replicase), which copies the viral RNA to form a double-stranded replicative form.  In turn, this dsRNA directs the formation of new viral RNA.
* Negative-sense ssRNA viruses (Group V) must have their genome copied by an RNA replicase to form positive-sense RNA. This means that the virus must bring along with it the enzyme RNA replicase. The positive-sense RNA molecule then acts as viral mRNA, which is translated into proteins by the host ribosomes.

[[Retrovirus]]es (Group VI) have a single-stranded RNA genome but, in general, are not considered RNA viruses because they use DNA intermediates to replicate. [[Reverse transcriptase]], a viral enzyme that comes from the virus itself after it is uncoated, converts the viral RNA into a complementary strand of DNA, which is copied to produce a double-stranded molecule of viral DNA. After this DNA is integrated into the host genome using the viral enzyme [[integrase]], expression of the encoded genes may lead to the formation of new virions.