ROLE OF THE FOWLPOX VIRUS THYMIDINE KINASE GENE FOR THE GROWTH OF FPVRECOMBINANTS IN CELL-CULTURE

Fowlpox virus (FPV) insertion plasmids were constructed that, upon int egration into the viral genome via in-vivo recombination, inactivate t he viral thymidine kinase (tk) gene. Using this approach, no wild-type virus-free stocks of recombinant virus could be obtained. In contrast , either integration of foreign genes into the intergenic region of th e intact FPV tk gene and the open reading frame located downstream, or the functional substitution of the inactivated FPV tk gene by an inta ct vaccinia virus tk gene resulted in the predicted stable recombinant s that were free of wild-type virus. Our results suggest that in alrea dy highly attenuated poxvirus strains an intact tk gene is essential f or efficient growth of the virus in cell culture.