Characterization of the vaccinia virus gene G

The regulation of elongation and termination of both prokaryotic and eukaryotic transcription is essential for appropriate gene expression. The modulation of the elongation potential of the RNA polymerase is affected by the action of many auxiliary factors. Vaccinia virus provides a system amenable to both genetic and biochemical study of transcriptional regulation. Little is known about the regulation of elongation and termination of viral transcription except early genes are specifically terminated and may be controlled at the stage of elongation. We believe that the vaccinia virus gene, G2R, encodes a protein whose function is critical to the regulation of the elongation potential of the viral RNA polymerase at late times during infection. The G2 mutant viruses display a defective late phenotype under nonpermissive condition which is manifested by the diminished quantity of large, late viral proteins. We have shown by analysis of viral RNA that the G2 mutant viruses produce late transcripts that are truncated at the 3$spprime$ ends. As a result, these transcripts are too short to encode large late viral proteins. The G2 protein is present in the infected cell at late times of infection though the G2R mRNA is made only at early times. The G2 protein was shown to interact, in vivo and in vitro, with the protein encoded by the H5R ORF of vaccinia virus. Additionally, the G2 protein was shown to interact in vivo with the protein encoded by the A18R ORF of vaccinia virus. To test the hypothesis that the G2 protein is necessary for elongation of transcripts from late promoters, we have begun phenotypic analysis of the G2 mutant viruses in vitro using an in vitro transcription elongation assay. Both genetic and biochemical data lead us to believe that the G2 protein functions in vivo as a late transcription elongation factor. To date, the biochemical characterization of the function of the G2 protein with respect to transcription elongation is in progress. Further in vitro experiments will be designed to functionally characterize the G2 protein.