In vitro and in vivo inhibition of primary transcription of vesicular stomatitis virus by a defective interfering particle.

A unique defective interfering (DI) particle, generated by a heat-resistant (HR) mutant of Indiana serotype vesicular stomatitis virus, was capable of inhibiting primary transcription by heterologous New Jersey serotype virions. The correlation between this phenomenon and the lowering of viral yields from doubly infected cells was investigated by the construction of chimeric DI particles containing the HR DI particle genome with a thermolabile polymerase. At the nonpermissive temperature, these DI particles were unable to self-transcribe, inhibit virion primary transcription, or reduce virion yield, but were able to be replicated. These results suggested that self-transcription of the HR DI particle genome was a prerequisite for heterotypic interference, but not for its own replication. Inhibition of virion primary transcription by HR DI ribonucleocapsids was also observed in vitro. At low HR DI to virion ribonucleocapsid ratios, the extent of inhibition was concentration dependent, whereas at high ratios, the amount of inhibition was concentration independent, approaching a limiting maximum value. A speculative mathematical model, which quantitatively accounts for these data, is presented. According to this model, the higher affinity for polymerase molecules by the HR DI ribonucleocapsids is explained in terms of dissociation events during transcription, which are more frequent in the longer virion ribonucleocapsids.