Equine Herpesvirus Type 1 Unique Short Fragment Encodes Glycoproteins with Homology to Herpes Simplex Virus Type 1 gD, gI and gE

Abstract

The nucleotide sequence of a 6.4 kbp portion of the 10-6 kbp BamHI fragment D contained in the unique short region of the equine herpesvirus type 1 (EHV-1) genome has been determined. Analysis of this sequence revealed five open reading frames (ORFs), four complete and one incomplete, which were encoded by the same sense strand. Comparison of the EHV-1 DNA sequence with that encoding glycoproteins of other alphaherpesviruses has revealed no significant homologies. Comparison at the amino acid level, however, has demonstrated regions of significant sequence similarity between the three complete EHV-1 ORFs 2, 3 and 4, and the herpes simplex virus type 1 (HSV-1) glycoprotein gD encoded by the US6 gene, the HSV-1 glycoprotein gI encoded by the US7 gene and the HSV-1 glycoprotein gE encoded by the US8 gene, respectively. The interrupted ORF 5 was found to display partial homology with the HSV-1 US9-encoded protein, but no homology was found between the protein encoded by ORF 1 and other proteins. The three collinear EHV-10RFs encoding putative glycoproteins with homology to the HSV-1 glycoproteins were therefore designated EHV-1 gD, gI and gE, respectively. Moreover, further similarities were found between EHV-1 gD and pseudorabies virus (PRV) gp50, between EHV-1 gI and PRV gp63 and varicellazoster virus (VZV) gplV, and between EHV-1 gE and PRV gI and VZV gpI. It is concluded that EHV-1, PRV, HSV-1 and VZV encode homologous glycoprotein genes in the small unique components of their genomes and that the genetic organization of these regions is conserved.

N-terminal sequence analysis of equine herpesvirus 1 glycoproteins D and B and evidence for internal cleavage of the gene 71 product

“…One exception is gene 71 (Telford et al, 1992) which has no known homologue in any of the herpesviruses sequenced to date, apart from the closely related EHV-4 (Nagesha et al, 1993). The signal cleavage sites of EHV-1 gD (Flowers et al, 1991;Audonnet et al, 1990;Whalley et al, 1991) and EHV-1 gB (Whalley et al, 1989) were predicted from deduced amino acid sequences using the (-3,-1) rule of von Heijne (1984) although these have not been verified by direct amino acid sequencing. EHV-1 gB is cleaved to yield subunits of approximately 76 and 54 kDa which are linked by disulphide bonds to form a 145 kDa heterodimer (Sullivan et al, 1989;Meredith et al, 1989).…”

Glycoprotein 60 of equine herpesvirus type 1 is a homologue of herpes simplex virus glycoprotein D and plays a major role in penetration of cells

“…This sequence was essentially the same as that of the Kentucky D strain (Audonnet et al, 1990), but differed at the C terminus from the Kentucky A sequence published by Flowers et al (1991). A 1242 bp HindlII fragment of the EHV-1 gD gene, corresponding to nucleotides 983 to 2221 of the Kentucky D sequence (Audonnet et al, 1990), was cloned into the HindlII site of pRSVori, a vector previously used for the expression of EHV-1 gB (Bonass et al, 1990), for expression under the control of the Rous sarcoma virus (RSV) long terminal repeat (LTR) promoter (Fig. 1).…”

“…The expressed gene product may lack the first six amino acids of the authentic signal sequence, if translation normally initiates at the preferred ATG codon at position 971 (Audonnet et al, 1990). It may be that this sequence is dispensable for the correct processing and localization of the protein, or that in vivo internal ATG residues operate to initiate translation, giving a mixed population of gD molecules.…”

“…This fragment contains an open reading frame and three potential initiation codons corresponding to those at positions 989, 992 and 1016. These three potential initiation codons lie within a hydrophobic region predicted to be the signal sequence (Audonnet et al, 1990). This fragment would be expected to encode all the amino acids found in the predicted mature protein.…”

“…Genes encoding six major glycoproteins have been mapped to the virus genome (Allen & Yeargan, 1987), but only one of these glycoproteins (gp17/18) maps to the short unique region. The region of the genome containing the gp17/18 gene has since been shown to contain three glycoprotein genes which are homologues of herpes simplex virus type 1 (HSV-1) genes encoding gE, gI and gD (Audonnet et al, 1990;Elton et aL, 1991), but the identity of gp17/18 remains to be established. Little is known about gp 17/18, although a monoclonal antibody (MAb) (5H6) directed against the protein passively protects hamsters against EHV-1 challenge (Stokes et al, 1989).…”