Transient expression system to measure the efficiency of vaccinia promoter regions

Vaccinia virus vectors: new strategies for producing recombinant vaccines

The development and continued refinement of techniques for the efficient insertion and expression of heterologous DNA sequences from within the genomic context of infectious vaccinia virus recombinants are among the most promising current approaches towards effective immunoprophylaxis against a variety of protozoan, viral, and bacterial human pathogens. Because of its medical relevance, this area is the subject of intense research interest and has evolved rapidly during the past several years. This review (i) provides an updated overview of the technology that exists for assembling recombinant vaccinia virus strains, (ii) discusses the advantages and disadvantages of these approaches, (iii) outlines the areas of outgoing research directed towards overcoming the limitations of current techniques, and (iv) provides some insight (i.e., speculation) about probable future refinements in the use of vaccinia virus as a vector.

Transient expression assay for qualitative assessment of gene expression by fowlpox virus

A transient expression assay for fowlpox virus (FPV) was developed to assess the feasibility of using heterologous promoters in FPV and to qualitatively determine relative promoter strength. A transient expression system for FPV has not been reported, and various methods used for transient expression in vaccinia-virus-infected cells produced negative results when used with FPV. Here a successful method for transient expression of E. coli beta-galactosidase in FPV-infected chick embryo fibroblasts is reported. This transient expression assay has been developed to qualitatively assess promoter recognition and gene expression by FPV. It should also prove useful in the identification of promoters from the FPV genomic library and in testing the accuracy of chimeric promoter-gene constructs.

Analysis of the fowlpoxvirus gene encoding the 4b core polypeptide and demonstration that it possesses efficient promoter sequences

The gene encoding the fowlpox virus 4b core polypeptide has been identified by analogy with the vaccinia 4b gene. It has been cloned, and its nucleotide sequence determined. The gene, which is 1971 nucleotides long, can encode a protein of 75,200 Da (75.2K polypeptide), slightly longer than its vaccinia counterpart with which it shares 52% identity. Sequences upstream of the fowlpox virus 4b gene correspond to the consensus sequence determined for vaccinia late promoters, suggesting that late promoter signals may be shared by the different genera of poxviruses. Upstream sequences have been cloned into a beta-galactosidase translational fusion vector and shown to promote the efficient expression of beta-galactosidase in a transient assay system. This expression was abolished in the presence of araC, an inhibitor of DNA replication which blocks late gene expression in poxviruses. The fowlpoxvirus 4b promoter should be a useful component of genetically engineered fowlpox virus vaccines.

Vaccinia virus recombinants expressing an 11-kilodalton beta-galactosidase fusion protein incorporate active beta-galactosidase in virus particles

Recombinant plasmids in which vaccinia virus transcriptional regulatory sequences were fused to the Escherichia coli lacZ gene were constructed for insertion of the lacZ gene into the vaccinia virus genome. beta-Galactosidase (beta-gal) was found in some purified recombinant vaccinia virions. By enzyme activity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and microscopic techniques, the evidence suggested that beta-gal accounted for 5% of the total protein in the virion. These recombinant viruses were constructed so that a portion of the coding sequences of a late vaccinia virus structural polypeptide was fused to the amino terminus of beta-gal to produce the fusion protein. Removal of the coding sequences resulted in the complete loss of beta-gal activity. This demonstrated that a vaccinia virus DNA segment from a late structural gene is responsible for the incorporation of beta-gal into the virion.