Abstract
The genome of a defective interfering particle (DILT) derived from the heat-resistant strain of vesicular stomatitis virus is expressed in vivo without the assistance of infectious helper virus. The rates of RNA synthesis in the presence of cycloheximide (primary transcription) are the same when infections are with equal numbers of physical particles of DILT or virus. With this treatment, DILT synthesizes only 12-17S mRNAs as characterized by size, polarity, and polyadenylylation. In the absence of cycloheximide, DILT-infected cells produce not only these mRNAs but also a 28S RNA species. This RNA, which represents one half of the viral specific RNA, contains newly synthesized full-length (+) and (-) strand DILT RNA. Both strands are found intracellularly as ribonucleoprotein complexes. Without cycloheximide present, the rate of RNA synthesis by DILT was less than that by virus. This curtailment is most likely due to the inability of DILT to synthesize L protein mRNA. An expanded role for defective interfering particles in infection is discussed.