Abstract
A defective-interfering (DI) particle of Sindbis virus was generated from a ts mutant of RNA- complementation group A by serially undiluted passages at 30 °C. This mutant induced interferon at a permissive temperature (30 °C), but not at a non-permissive temperature (40.5 °C); it also expressed homotypic interference throughout the range 30 to 40.5 °C. This demonstrates for the first time in a DI particle a ts function, namely, the ability to induce interferon. In addition, our data provide further evidence that the RNA genome of a Sindbis DI particle can be translated within the cell. We postulate that the products of translation function to produce the putative inducer of interferon, namely a molecule of dsRNA.