The identification of an African swine fever gene with conserved helicase motifs and a striking homology to herpes virus origin binding protein, UL9

Abstract

African swine fever virus (ASFV), the causative agent of African swine fever in domestic pigs (3,8,12), is a large icosahedral virus with a double stranded DNA genome of (14) and gene 19R of human herpes virus 6-HH6 (9). Furthermore, each of six highly conserved motifs identified for the helicase superfamily (7) and required for function of the origin binding protein (UL9) of HSV1 are conserved in LMW6DL (10). Sequence analysis with the FASTA algorithm (13) shows LMW6DL most closely related to HH6 (28.5% amino acid identity/341 residues; 51.3% similarity, FASTA = 289, z = 25.2), followed by VZV (25.9% amino acid identity/312 residues; 51.7% similarity, FASTA = 177, z = 15.4), HSV1 (27.5% amino acid identity/325 residues; 50.7% similarity, FASTA = 126, z = 10.6) and EHSV 1 (26.8 % amino acid identity/325 residues; 51.2% similarity, FASTA = 139, z = 1 1.5). The aligment of each of the six highly conserved motifs is shown in Figure 1. UL9 of Herpes simplex virus is essential for viral DNA replication, codes for a protein that specifically recognizes sequences within the viral origin of replication, and possesses independent helicase and DNA-dependent ATPase activities (10). The striking relationship between LMW6DL and the Herpes virus origin binding protein indicates a possible role for this gene product in ASFV DNA replication.

Human herpesvirus 6 (strain U1102) encodes homologues of the conserved herpesvirus glycoprotein gM and the alphaherpesvirus origin-binding protein

“…l b) (J. Nicholas, unpublished results). The 19R protein has significant amino acid sequence homology to the origin-binding proteins (OBP) encoded by the alphaherpesviruses HSV-1, VZV and EHV-1 and to a protein encoded by African swine fever virus (ASFV; optimized FASTA score 289; Sussman et al, 1993), but it appears not to share any significant amino acid sequence similarity with the predicted translation products of the positionally analogous ORFs encoded by the betaherpesviruses HCMV or murine CMV (W. Rawlinson, personal communication), or the gammaherpesviruses EBV (Baer et al, 1984) and HVS (Albrecht et al, 1992). The high degree of amino acid sequence conservation shared by the HHV-6, HSV-1, VZV and EHV-1 protein homologues, together with the lack of any detectable amino acid sequence similarity between these protein sequences and those encoded by members of the beta-and gammaherpesviruses, suggests possible structural similarities between the HHV-6 origin of lytic cycle DNA replication (oriLyt) and the small ATrich alphaherpesvirus ori elements (Weller et al, 1985;Stow & Davison, 1986;Robertson et al, 1991), rather than with the larger and more complex EBV (Hammerschmidt & Sugden, 1988), HCMV and simian CMV oriLyt elements (Hamzeh et al, 1990;Anders & Punturieri, 1991 ;Anders et al, 1992).…”

“…2) reveals the presence of six conserved motifs within the N-terminal regions of each of the proteins which are predictive of helicase activity (Gorbalenya et al, 1989;Martinez et al, 1992;Sussman et al, 1993). Several studies have shown that the HSV-1 OBP has DNA helicase and associated DNA-dependent ATPase activities in addition to its origin-binding activity (Fierer & Challberg, 1992).…”

“…Origin recognition and binding activities of both the HSV-I and VZV OBPs appear to be located within the C-terminal one-third of these proteins (Weir et al, 1989;Stow et al, 1990;Deb & Deb, 1991;Arbuckle & Stow, 1993), although the specific binding sites of the two proteins on their respective origins of replication do differ (Stow et al, 1990). Each of the herpesvirus-encoded OBP homologues exhibit a lower degree of amino acid sequence con- (Sussman et al, 1993). The consensus sequence was derived from the alignment of herpesvirus-encoded homologues where conservative amino acid changes are indicated by the symbol '*' and are grouped (IVLM), (FYW), (RKH), (DENQ) and (CSTGAP).…”

“…HHV-6 is phylogenetically more closely related to HCMV than it is to members of the alphaherpesvirus subgroup [e.g. herpes simplex virus type 1 (HSV-1; McGeoch et al, 1988), varicella-zoster virus (VZV; Davison & Scott, 1986), equine herpesvirus 1 (EHV-1 ; Telford et al, 1992)] or the gammaherpesvirus subgroup [e.g. Epstein-Barr virus (EBV; Baer et al, 1984), herpesvirus saimiri (HVS; Albrecht et al, 1992)].…”