A consideration of previously uncharacterized fowl poxvirus unidirectional and bidirectional late promoters for inclusion in homologous recombinant vaccines

Abstract

Because of the limited analysis of fowl poxvirus (FPV) promoters, expression of foreign proteins by recombinant FPV has usually been directed by heterologous vaccinia virus or synthetic poxvirus promoters. Thus, the impact of completely homologous recombinant virus vaccines has yet to be realized by the poultry industry. In an effort to increase the availability of such transcriptional regulatory elements, the modulation of gene expression by six previously uncharacterized FPV late promoters was examined. To simplify this comparison, each promoter region was separately coupled to the same reporter gene (lacZ) in individual plasmid constructs, and their activities in transfected, virus-infected cells were monitored. In each of the four selected unidirectional transcriptional regulatory elements as well as a 30-base pair representative of the bidirectional promoter region, the predicted temporal specificity of expressing at late stages of virus replicative cycle was verified. Stable lacZ gene transcripts arising from each plasmid varied less than threefold in quantity, whereas the amounts of beta-galactosidase product ranged within a 130-fold interval. Only the promoter that naturally regulates expression of the A type inclusion body protein gene directed production of beta-galactosidase at a level comparable with that associated with the strong vaccinia virus P11 promoter. Because one of the remaining unidirectional transcriptional regulatory elements, P174, was only 2.4-fold less efficient, both of these promoters, P174 and P190, should be satisfactory for directing the expression of poultry pathogen genes inserted into the genomes of FPV recombinant vaccines.