Poxviruses differ from the other major groups of DNA viruses with regard to their use of the cytoplasm, rather than the nucleus, as the site of transcription. Consistent with this strategy, poxviruses encode their own DNA-dependent RNA polymerase as well as many—if not all—of the additional enzymes and factors needed to synthesize functional capped, methylated, and polyadenylated mRNA. Furthermore, all of the factors necessary for transcription of the early class of genes are packaged within the virus particle allowing viral mRNA to form within minutes after infection. A cascade of events follows involving DNA replication and the synthesis of an assortment of trans-acting factors and leading to the expression of successive classes of viral genes.