Herpes Simplex Virus Type 1 U_L34 Gene Product Is Required for Viral Envelopment

ABSTRACT

The herpes simplex virus type 1 U_L34 gene encodes a protein that is conserved in all human herpesviruses. The association of the U_L34 protein with membranes in the infected cell and its expression as a gamma-1 gene suggest a role in maturation or egress of the virus particle from the cell. To determine the function of this gene product, we have constructed a recombinant virus that fails to express the U_L34 protein. This recombinant virus, in which the U_L34 protein coding sequence has been replaced by green fluorescent protein, forms minute plaques and replicates in single-step growth experiments to titers 3 to 5 log orders of magnitude lower than wild-type or repair viruses. On Vero cells, the deletion virus synthesizes proteins of all kinetic classes in normal amounts. Electron microscopic and biochemical analyses show that morphogenesis of the deletion virus proceeds normally to the point of formation of DNA-containing nuclear capsids, but electron micrographs show no enveloped virus particles in the cytoplasm or at the surface of infected cells, suggesting that the U_L34 protein is essential for efficient envelopment of capsids.