Action of interferon: kinetics and differential effects on viral functions

A highly purified rabbit interferon was tested for its capacity to inhibit various manifestations of infection of primary rabbit kidney (RK) cells with vesicular stomatitis (VS) virus. A kinetic analysis of the actinomycin-sensitive phase of interferon-induced cellular resistance revealed that RK cells could transcribe virtually all of the hypothetical antiviral messenger ribonucleic acid (mRNA) within 3 hr. Similar exposure to interferon reduced virus yield by 95 to 99% and markedly inhibited cytopathic effect on RK cells infected at a multiplicity of 10 or less. Interferon was less effective in blocking cytopathic effects when RK cells were infected at a multiplicity of 100. However, RK cells pretreated with the same amount of interferon and infected at a multiplicity of 100 failed to incorporate (3)H-amino acids into structural or nonstructural proteins of VS virus identified by polyacrylamide gel electrophoresis. Despite this inhibition of viral protein synthesis, interferon did not prevent the switch off by VS virus of cellular protein synthesis. The rapidity with which a high multiplicity of VS virus switched off cellular protein synthesis, even in cells rendered resistant to viral infection by interferon, is further evidence that this reaction is caused by an infecting virion component rather than by a newly synthesized viral product.

Proteins of vesicular stomatitis virus: kinetics and cellular sites of synthesis

FIVE VIRAL PEPTIDES SYNTHESIZED IN L CELLS INFECTED WITH VESICULAR STOMATITIS (VS) VIRUS WERE IDENTIFIED BY POLYACRYLAMIDE GEL ELECTROPHORESIS AND DESIGNATED AS FOLLOWS: nucleoprotein N, a membrane glycoprotein G, a membrane surface protein S, and two nonstructural proteins NS1 and NS2. A slowly migrating minor structural protein L also present in infected cells is probably an aggregate. Incorporation of (3)H-amino acids into each viral protein could be detected by the 2nd hr after infection and even earlier for protein N which is synthesized in the greatest amount. There was no evidence of regulation of viral protein synthesis at the transcriptive level; nonstructural and structural proteins were synthesized throughout the cycle of infection. Short pulses of (3)H-amino acids revealed no uncleaved precursor peptides that could be chased into structural peptides. Proteins N and S were chased into released virions but protein G was apparently incorporated into virions as it was being synthesized. VS viral proteins of infected cells were released by mechanically disrupting cytoplasmic membrane by nitrogen decompression and fractionated by high-speed centrifugation. Protein NS1 was present in the nonsedimentable cytoplasmic fraction throughout the cycle of infection. The nucleoprotein N was recovered primarily from the nonsedimentable fraction early in infection but aggregated into a sedimentable component, presumably the nucleocapsid, later in infection. Proteins G and S were always present in the sedimentable fraction of mechanically disrupted infected cells, presumably in association with plasma membrane. Exposure of infected cells to the membrane-dissolving agent, digitonin, resulted in solubilization of most of protein G and all of protein S but not of protein N. These experiments are compatible with the hypothesis that VS viral proteins G and S are synthesized at and inserted into plasma membrane which envelopes a nucleocapsid core to form the VS virion.

Purified rabbit interferon: attempts to demonstrate interferon-specific 3H-protein

(3)H-protein present in highly purified preparations of rabbit interferon was not conclusively separated from noninterferon, cellular (14)C-proteins by co-chromatography on carboxymethyl-Sephadex or by co-electrophoresis on acid or neutral polyacrylamide gels.