Effect of interferon on polymerization of single-stranded and double-stranded mengovirus ribonucleic acid

Antiviral activity of 3-methyleneoxindole

3-Methyleneoxindole (MO), an oxidation product of the plant auxin indole-3-acetic acid, can selectively inhibit the replication of herpes-, mengo-, polioviruses, and Sindbis virus. The antiviral action of MO, a sulfhydryl binding compound, is neutralized by 2-mercaptoethanol if the latter is added soon after exposure of infected cells to MO. If addition of 2-mercaptoethanol is delayed, the antiviral action of MO appears to be irreversible. Data are presented which indicate that the antiviral action of MO is not mediated by interferon.

Viral ribonuclei acid synthesis by Newcastle disease virus mutants isolated from persistently infected L cells: effect of interferon

The synthesis of different viral ribonucleic acid (RNA) species was studied in chick embryo (CE) and mouse L-cell cultures infected with the Herts strain of Newcastle disease virus (NDV(o)) and a mutant isolated from persistently infected L cells (NDV(pi)). In CE cell cultures, both viruses synthesized significant amounts of 54, 36, and 18S RNA. However, in L cells, synthesis of 54S virion RNA was markedly reduced. From these results, it seems likely that the low yield of infective virus in L cells is due to a deficient synthesis of 54S RNA in this host. On this basis, however, it is apparent that the "covert" replication of NDV(o) in L cells is due to factors other than viral RNA synthesis. When low concentrations of interferon were used to pretreat CE cells, a differential effect on the synthesis of various RNA species was observed. The 18S RNA of NDV(o) was more sensitive to interferon action than the 36 and the 54S RNA species. In contrast, the 18S RNA of NDV(pi) was less sensitive than the 36S and the 54S RNA. The inhibition of 54S RNA synthesis correlated with the reduction of viral yield and explained the greater sensitivity of NDV(pi) to interferon.

Rapid sensitive assay for interferons based on the inhibition of MM virus nucleic acid synthesis

A method for assaying mouse interferon based on the inhibition of viral ribonucleic acid (RNA) synthesis was devised. The amount of MM virus and RNA synthesized in interferon-treated L-cell cultures was determined by measuring the amount of (3)H-uridine converted into a trichloroacetic acid-insoluble form after treatment of the infected cultures with 2.5 mug of actinomycin D per ml. The amount of RNA synthesized was inversely related to the concentration of interferon used for treatment. A linear dose-response regression curve was obtained by plotting the log of the amount of RNA made, expressed as a percentage of the control, versus the log of the reciprocal of the interferon dilution. A unit of interferon was defined as that concentration which inhibited nucleic acid synthesis by 50% (INAS(50)). The concentration of mouse interferon could be determined within 24 hr. This assay method, on the average, was approximately half as sensitive as the method which measured the 50% reduction of MM virus plaque number (PDD(50)-MM method), but was, on the average, almost 1.7 times as sensitive as the PDD(50)-VSV method. It averaged approximately 20 times the sensitivity of the methods which used as end points the 70% reduction in yield of MM virus or the complete inhibition of cytopathic effect by MM virus. The reproducibility of the INAS(50) technique was tested in two ways. (i) Four independent assays of an interferon specimen were performed with replicate cultures. The standard deviation was 11.2% of the mean titer. (ii) On different dates, one interferon specimen was assayed seven times and another was assayed four times. The standard deviations were 21.5 and 26.6% of the respective mean titers.

Effect of interferon on deoxyribonuclease induction in chick fibroblast cultures infected with cowpox virus

An exonuclease which degrades native deoxyribonucleic acid at pH 9.2 was induced in chick embryo fibroblast cultures and in human amnion cells by infection with cowpox virus. Highly purified chick embryo interferon suppressed the induction of the enzyme in the homologous cell system but not in the human amnion cell cultures. "Mock" interferon prepared from uninfected chicken eggs and purified in the same manner as biologically active interferon preparations had no effect on the induction of the enzyme.