Insertional inactivation of the vaccinia virus 32-kilodalton gene is associated with attenuation in mice and reduction of viral gene expression in polarized epithelial cells.

The mechanism of poxvirus attachment to cells is poorly understood. We have identified a 32-kDa envelope protein of vaccinia virus which binds to the surface of cultured cells. This binding is specific and selective (J.-S. Maa, J. F. Rodriguez, and M. Esteban, J. Biol. Chem. 265:22174-22180, 1990; C. Lai, S. Gong, and M. Esteban, J. Virol. 65:499-504, 1991). In this investigation, we studied the effect of inactivating the 32-kDa gene (32K gene) on the biology of vaccinia virus. We show that inactivation of the 32K gene decreases by 80% the mortality of mice infected with 32K- vaccinia virus. This reduction in mortality correlates with diminished viral gene expression in target tissues. In highly polarized epithelial cells, viral gene expression of 32K- virus was reduced (50 to 60%) at both the apical and basolateral surfaces in comparison with a 32K+ virus. Restriction of virus gene expression in polarized cell surfaces occurs for both intracellular and extracellular forms of infectious 32K- vaccinia virus. The two infectious forms of vaccinia virus 32K+ infect polarized cells preferentially by the basolateral surface. Our findings provide evidence of the importance of the 32-kDa protein in viral pathogenesis.