Poxvirus Gene Expression and DNA Replication

National Institute Of Allergy And Infectious Diseases

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Abstract

Poxviruses encode enzymes and factors needed for transcription and replication of their genomes within the cytoplasm of infected cells. Vaccinia virus, the prototypic member of the poxvirus family, provides a unique system for combining biochemical and genetic approaches for investigating mechanisms of gene regulation, mRNA biosynthesis and DNA synthesis. Studies with vaccinia virus indicated that the genes are divided into three temporal classes - early, intermediate and late. Each gene class has a consensus DNA promoter sequence and corresponding transcription factors that interact with the virus-encoded multisubunit RNA polymerase. The transcription system for early genes is packaged within the infectious virus particle during its assembly, whereas the factors for intermediate and late gene transcription are synthesized successively after infection and localize within cytoplasmic factory areas. Of the three transcription factors, only the early has been well studied. We are now investigating the intermediate and late factors. We previously determined that the intermediate factor is comprised of two subunits encoded by the A8 and A23 genes. Using the AlphaFold protein structure prediction program and the DALI structural similarity search, we found previously unknown homology to the eukaryotic transcription factor IIB and the TATA-binding protein, respectively. Furthermore, the Colabfold advanced prediction program suggests that the two subunits interact with a large space in the center that likely holds DNA. Efforts are now being made to confirm the functional interactions of the complex. An understanding of the regulation of poxvirus gene expression and DNA replication will help to design vaccines and identify targets for antiviral therapy and will contribute to our understanding of these processes in other viruses and cells.