IV: Single-stranded (+)sense RNA (Picornaviruses; Togaviruses, etc)
a) Polycistronic mRNA e.g. SARS, Picornaviruses; Hepatitis A and C (NOTE Hepatitis B virus does not belong to this class), polio. Genome RNA = mRNA. Means naked RNA is infectious, no virion particle associated polymerase. Translation results in the formation of a polyprotein product, which is subsequently cleaved to form the mature proteins.