Fig. 2.4.

Replication of ssRNA virus genomes. ssRNA + and ssRNA– genomes must be transcribed (T) by the viral RdRp to form the dsRNA-replicative intermediate. The resulting antigenomes can then be transcribed by the RdRp to form replicative intermediates that can yield additional genome RNAs. Regulated asymmetries in transcription initiation enable production of appropriate quantities of genome and antigenome strands at different stages of virus replication. ssRNA + genomes and ssRNA– antigenomes have polarities suitable for translation of viral proteins. Viruses employ a variety of mechanisms to generate 5’ structures that enable some RNA + molecules to function as mRNAs. RNA + molecules are drawn in black and RNA– molecules are in gray. Balls on the ends of RNAs signify 5’ ends, and arrows signify 3’ ends.