11 - Introduction to RNA viruses

Abstract

Most RNA viruses replicate using virally encoded RNA-dependent RNA polymerase (RdRp). These viruses likely arose from a common ancestor and are grouped in the Realm Riboviria. During replication, three types of RNA are synthesized: the genome, a copy of the genome, and mRNAs. The riboviruses can be subdivided based on the type of RNA that serves as the genome. Positive or plus (+)-strand RNA viruses have genomes that are functional mRNAs. There are three groups of RNA viruses whose genomes are not mRNAs. They are the negative- or minus-strand RNA viruses, the closely related ambisense RNA viruses, and double-stranded RNA viruses. For each of these groups of viruses, the first synthetic event after genome penetration is transcription. This is accomplished by viral proteins (including the RdRp) that enter cell with the genome. One small group of viruses (Realm Ribozyviria) have RNA genomes that are replicated by cellular polymerases.