Identification and structure of the Marek's disease virus serotype 2 glycoprotein M gene: comparison with glycoprotein M genes of Herpesviridae family.
We determined the nucleotide sequence of a portion of BamHI-C fragment of Marek's disease virus serotype 2 (MDV2) strain HPRS24 which was suspected to contain the homologue of the herpes simplex virus type 1 (HSV-1) gene UL10, encoding glycoprotein M (gM). An open reading frame whose translation product exhibited significant similarities to HSV-1 gM protein and respective proteins of other herpesviruses of 37.5% and 45.5% to 31.8%, respectively, was identified. A number of distinct transcriptional consensus sequences were found upstream of the first putative start codon of MDV2 UL10 protein. In transcriptional analysis, the gene was transcribed into an 1.5 kb RNA. The primary translation product comprises 424 amino acids with a predicted molecular weight of 46.9 kDa. The predicted MDV2 UL10 protein contains eight hydrophobic domains with sufficient length and hydrophobicity to span the lipid bilayer conserved in the genomes of all herpesviruses which have been sequenced so far. In the region located between the first and second hydrophobic domains, two potential N-linked glycosylation sites were presented. Interestingly, highly charged residues were abundantly possessed in the carboxy-terminal part of the MDV2 UL10 protein. By comparison of the amino acid sequence of the MDV2 UL10 gene with the homologues from other herpesviruses, the data might contribute for further evidence of the evolution of herpesviruses from a common progenitor and an ancient example of MDV2 belonging to the Alphaherpesvirinae subfamily. In addition, the existence of corresponding genes in human, mammalian, and avian herpesvirus genomes, suggests indirectly an important role for gM in the natural life cycle of the virus.