Cellular localization of Saint Louis encephalitis virus replication

Replication of Saint Louis encephalitis (SLE) virus was inhibited when PS cells were treated with actinomycin D, daunomycin or cordycepin during the first 9 hr after infection. Autoradiography of SLE virus-infected pulse labelled cells demonstrated that viral RNA synthesis is localized within the nuclear area. Nuclei purified from cells after 12 hr of infection contained heterogeneous 20 S to 26 S viral RNA but no SLE virus genome sized 43S RNA. Later during infection, nuclei isolated from infected cells contained large amounts of 43 S and 20 S to 26 S RNAs. The 43 S viral RNA present in cells late in infection could not be removed with 1% Tween 80: Nonidet P 40. Purified nuclei isolated from cells early in infection supported the synthesis of 43 S virion RNA in the absence of cytoplasmic factors. The cytoplasmic membrane fraction prepared from cells early in infection contained heterogeneous 10 S to 26 S RNA species; later during infection these membranes contained viral 43 S, 26 S to 30 S and 4 S RNA. These results suggest that the nucleus is an important site of early viral synthesis.