Herpes simplex virus type 1 U(L)34 gene product is required for viral envelopment

The herpes simplex virus type 1 U(L)34 gene encodes a protein that is conse rved in all human herpesviruses. The association of the U(L)34 protein with membranes in the infected cell and its expression as a gamma-1 gene sugges t a role in maturation or egress of the virus particle from the cell. To de termine the function of this gene product, we have constructed a recombinan t virus that fails to express the U(L)34 protein. This recombinant virus, i n which the U(L)34 protein coding sequence has been replaced by green fluor escent protein, forms minute plaques and replicates in single-step growth e xperiments to titers 3 to 5 log orders of magnitude lower than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 t o the point of formation of DNA-containing nuclear capsids, but electron mi crographs show no enveloped virus particles in the cytoplasm or at the surf ace of infected cells, suggesting that the U(L)34 protein is essential for efficient envelopment of capsids.