Synthesis of Saint Louis Encephalitis Virus Ribonucleic Acid in BHK-21/13 Cells

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Abstract
Infection of baby hamster kidney cells (BHK-21/13) with Saint Louis encephalitis (SLE) virus depressed the rate of protein and ribonucleic acid (RNA) synthesis until viral RNA synthesis began 6 hr postinfection (PI). Virus-directed RNA synthesis was subsequently inhibited until 12 hr PI when virion maturation began. The rate of protein synthesis reached a peak 6 hr PI and was subsequently depressed until just before the onset of virion maturation. Density gradient analysis of phenol-extracted RNA from actinomycin-treated infected cells indicated that, at 6 to 8 hr and again at 12 to 20 hr PI, three species of viral-specific RNA were synthesized. The most rapid sedimenting form (43 S ) was ribonuclease-sensitive and had a base composition similar to the RNA isolated from mature virions. The 20 S RNA species was ribonuclease-resistant and had a sedimentation coefficient and base composition similar to the replicative form associated with other arbovirus infections. The 26 S RNA was ribonuclease-resistant (0.2 μg/ml, 0.1 m NaCl, 25 C, 30 min) and had a nucleotide base composition closer to the 20 S form than to the values for 43 S RNA. Five-minute pulse labeling of infected cultures during the period viral RNA synthesis was maximal resulted in labeling of only the 20S to 22S RNA fractions. With pulse-labeling periods of 10 min, both the 20 S and 26 S RNA species were radioactive. Periods of radioactive labeling of as long as 15 min were required before the 43 S form was radioactively labeled. These results suggest that the 20 S and 26 S RNA may be intermediate forms in the synthesis of 43 S viral RNA.