Abstract
The RNA of a unique long defective interfering particle (DI-LT2) derived from the heat-resistant strain of vesicular stomatitis virus (VSV) contains 70 nucleotides at its 3' end that are complementary to the 5' end of the VSV RNA. Following this region of terminal complementarity, there is a precise copy of the 3' end of the nondefective VSV RNA. The sequence homology between the DI-LT2 RNA and the 3' end of VSV RNA extends for at least 60 bases and probably for most of the length of the DI-LT2 RNA. The DI-LT2 particle is capable of transcription in vitro but produces only a short RNA [defective interfering (DI) particle product], which is encoded by the extreme 3' terminus of the DI RNA. Neither leader RNA nor capped VSV mRNAs are synthesized by DI-LT2, although competent templates for these are present. These data suggest that the 3'-terminal initiation is a prerequisite of the production of competent transcripts and that the sequence coding for leader RNA is not, by itself, sufficient for initiation. We propose a model for the origin of this DI particle, involving specific termination and resumption of replication, which is similar to that described previously for another class of DI particle RNAs.