Once a host cell is infected with a virus, it is necessary for the virus to replicate in order to continue the infection cycle of additional host cells.  Once the virus has transported itself inside the host cellís cellular walls, the viral (+) ssRNA is translated by the hostís ribosomes.  The complex of the ribosomes and the (+) ssRNA will assemble three virus specific proteins, the third of which is the enzyme RNA-polymerase.  The RNA-polymerase will then synthesize a (-) ssRNA strand that is complimentary.  This newly synthesized (-) ssRNA strand will then serve as the template for replicating additional (+) ssRNA.  In other words, replication is semiconservative where the parental vRNA serves as a template for transcription of complimentary strands, cRNAs.  The cRNA then are utilized as templates to recreate vRNA strands.  This entire process is catalyzed by RNA-dependent RNA, or replicase.  The gene coding for the viral polymerase is located at the C terminal end of the template RNA and is synthesized last.  The 3í end is the terminus that must bind to begin the first round of replication.
 
 

Viral polymerases can be classified into three different groups: DNA-dependent RNA polymerase, RNA-dependent DNA polymerase, and RNA-dependent RNA polymerase.
 
 
 
 

Structure: