TRANSCRIPTION AND REPLICATION STRATEGIES OF RNA VIRUSES

Family	Genome	Viral transcriptase	Protein product
Picornaviridae Flaviviridae Togaviridae Caliciviridae	(+)ssRNA*	genomic RNA serves as mRNA; encoded RNA-dependendent RNA polymerase (RDRP) for genomic (+)ssRNA synthesis via (-)ssRNA	polyprotein cleaved into smaller viral proteins
Coronaviridae	(+)ssRNA	encoded RDRP for the synthesis of genomic RNA and subgenomic, monocistronic, mRNA	viral protein
Paramyxoviridae Rhabdoviridae Filoviridae	(-)ssRNA	encoded RDRP for the synthesis of subgenomic, monocistronic, mRNA [ (+)ssRNA] , and full length (+)ssRNA as a template for genomic (-)ssRNA	viral protein
Orthomyxoviridae	Segmented (-)ssRNA	encoded RDRP; strategy as above	viral protein
Arenaviridae Bunyaviridae	Segmented (+, -)ssRNA	encoded RDRP; mixed strategy	viral protein
Reoviridae	Segmented dsRNA	encoded RDRP; (-)RNA serves as a template for mRNA; (+)RNA serves as a template for genomic RNA	viral protein
Retroviridae	Two copies of (+)ssRNA	encoded RNA-dependent DNA polymerase; see the life cycle of HIV	regulatory protein as viral protein; structural viral protein as polyprotein

^*(+)ssRNA = positive or sense single stranded RNA; (-)ssRNA = negative or antisense ssRNA; (ds)RNA = double stranded RNA with both positive/negative strands, i.e., complementary nucleotide sequences. By convevtion, the noncoding strand of DNA is designated as the (+) or sense strand, while the coding (transcribed) strand is designated as the (-) or antisense strand. Thus, (+) strand RNA can serve as mRNA for protein synthesis and is similar in sequence to the noncoding (+) strand of DNA.