Site of foot-and-mouth disease virus-ribonucleic acid synthesis and some properties of its double-stranded ribonucleic acid

Abstract Foot-and-mouth disease virus (FMDV) RNA is synthesized in the cytoplasm of the baby hamster kidney cell. This conclusion is based on the distribution within the subcellular fractions of [ 3 H]uridine pulse-labeled virus-specific RNA, and of FMDV-induced RNA polymerase activity. Three classes of virus-specific RNA are defined by sedimentation rate in sucrose gradients: a 37-S viral RNA, a 20-S ribonuclease-resistant RNA, and a heterogeneous RNA (peak sedimentation rate between 18 and 28-S ribosomal RNA). All three classes were isolated from the cytoplasm. The 20 S and 37 S are infectious. The 20-S RNA has properties of double-stranded RNA since its resistance to ribonuclease is dependent on salt concentration and is destroyed by boiling at 100°. The ratio of double-stranded RNA to single-stranded RNA increases during the replication cycle. In accord with this, FMDV polymerase from cells harvested late in the replication cycle catalyzes the cell-free synthesis of relatively less 37-S viral RNA and more double-stranded RNA (and heterogeneous RNA) than FMDV polymerase preparations from cells harvested early in the cycle.