IDENTIFICATION AND CHARACTERIZATION OF A MAREKS-DISEASE VIRUS GENE HOMOLOGOUS TO GLYCOPROTEIN-L OF HERPES-SIMPLEX VIRUS

We have identified three Marek's disease virus (MDV) open reading fram es (ORFs) within the BamHI D fragment of MDV genome. The predicted pol ypeptides are homologous to UL1 (glycoprotein L, gL), UL2 (uracil-DNA glycosylase), and UL3 (nuclear localizing phosphoprotein) of herpes si mplex virus type 1 (HSV-1). Comparison of the deduced amino acid seque nces of these three ORFs with HSV-1 counterparts revealed overall iden tities of 18, 43, and 49%, respectively. In spite of the low overall a mino acid identity with HSV-1 gL, the first open reading frame was ide ntified as a gL homolog of HSV-1 based not only on the gene arrangemen t but also on a limited amino acid conservation among gL homologs of a lpha-herpesviruses. To characterize the expression of the MDV gL gene, an antiserum to a hydrophilic region of the gene expressed in a bacte rial expression vector was produced. Immunoprecipitation with this ant iserum revealed a 25,000-Da polypeptide in MDV-infected cells. Further more, the 25,000-Da polypeptide migrated as a 18,000-Da polypeptide fo llowing PNGase F treatment. This result is consistent with the predict ed molecular weight of MDV gL, considering the two potential N-glycosy lation sites and the predicted N-terminal signal sequence. A recombina nt fowlpox virus expressing the MDV gL gene was generated to character ize this glycoprotein. Unlike gL in MDV-infected cells, gL expressed b y recFPV-gL was highly sensitive to Endo H, indicating that it was pro bably retained in the endoplasmic reticulum and was not properly proce ssed to a mature form. Therefore, similar to HSV-1, coexpression and c omplex formation of MDV gL and gH may be required for proper processin g and transport of gL to the cell surface.