Abstract
Virus ribonucleic acid molecules are known to induce formation of interferon. Previous reports have demonstrated the inducing activity of the double-stranded RNA extracted from reovirus (Tytell, et al. 1967), or of double-stranded RNA formed within cells infected with RNA or DNA viruses (Field, et al. 1967; Skehel & Burke, 1968; Falcoff & Falcoff, 1969; Colby & Duesberg, 1969). Gandhi & Burke (1970), using u.v.-irradiated fowl plague or Newcastle disease viruses, showed that interferon production occurred in the absence of any detectable RNA synthesis, and the authors suggested that the single-stranded RNA of the virus was the inducer of interferon formation. Lomniczi & Burke (1970) arrived at a similar conclusion using Semliki Forest virus as an inducer. However, Huppert, Hillova & Gresland (1969) reported that u.v.-irradiated Newcastle disease virus which was totally unable to produce infectious virus was still able to synthesize virus RNA in infected cells, as detected by a hybridization method.