A mutant herpes simplex virus type 1 unable to express glycoprotein L cannot enter cells, and its particles lack glycoprotein H.

Herpes simplex virus type 1 (HSV-1) glycoprotein H (gH) is essential for virus entry into cells and forms a hetero-oligomer with a newly described viral glycoprotein, gL. Normal folding, posttranslational processing, and intracellular transport of both gH and gL depend upon the coexpression of gH and gL in cells infected with vaccinia virus vectors (L. Hutchinson, H. Browne, V. Wargent, N. Davis-Poynter, S. Primorac, K. Goldsmith, A. C. Minson, and D. C. Johnson, J. Virol. 66:2240-2250, 1992). Homologs of gH and gL have been found in herpesviruses of all subgroups, and thus it appears likely that the gH-gL complex serves a highly conserved function during herpesvirus penetration into cells. To examine the role of gL in the infectious cycle of HSV-1, a mutant HSV-1 unable to express gL was constructed by inserting a lacZ gene cassette into the coding sequences of the UL1 (gL) gene. Because gL was found to be essential for virus replication, cell lines capable of expressing gL were constructed to complement the virus mutant. In the absence of gL, virus particles were produced, and these particles reached the cell surface; however, gL-negative particles purified from infected cells were also deficient in gH. Mutant virions lacking gH and gL were able to adsorb onto cells but were unable to enter cells and initiate an infection. Further, the role of gL in fusion of infected cells was reexamined. A mutation in HSV-1 (804) which produces the syncytial phenotype had previously been mapped to a region of the HSV-1 genome which includes the UL1 gene and no other open reading frame. However, in contrast to this previous report, we found that the syncytial mutation in 804 affects the UL53 gene, which encodes gK, a gene commonly mutated in syncytial viruses.