Unique mode of transcription in vitro by Vesicular stomatitis virus

In addition to the five mRNA species and 47 nucleotide long leader RNA synthesized by purified virions of vesicular stomatitis virus, at least three discrete low molecular weight RNA species having approximate chain lengths of 28, 42 and 70 nucleotides can be detected in vitro. Each of these RNA species displays a unique and characteristic T1 fingerprint profile and contains (p)ppAA as its 5' terminus. By partial sequence analyses, two of the small RNA products, 42 and 28 bases long, were found to contain 5' terminal sequences identical to those in the N and NS mRNAs, respectively. Ultraviolet inactivation studies demonstrate that each of these RNA species has a target size in agreement with its molecular weight indicating independent initiation. Kinetic studies show that the small RNA species are synthesized within 1 min, while mRNA chain completion occurs later in the sequential order N-NS-M-G. These results indicate that viral mRNA synthesis occurs in vitro by multiple initiations at different promoter sites on the genome RNA, and that the elongation and completion of the individual mRNAs depend on prior transcription of 3' proximal genes. We present a model for viral mRNA synthesis in vitro.