Complete Genomic Sequence and Phylogenetic Analysis of the Lactate Dehydrogenase-Elevating Virus (LDV)

The apparently complete sequence of the RNA genome of the neurovirulent isolate of lactate dehydrogenase-elevating virus (LDV-C) has been determined. The LDV-C genome is at least 14,222 nucleotides in length and contains eight open reading frames (ORFs). ORF 1a, which encodes a protein of 242.8 kDa and is located at the 5′ end of the genome, contains at least two putative papain-like cysteine protease domains, and one putative chymotrypsin-like serine protease domain. This ORF terminates with a UAG stop codon that can be bypassed if a -1 frameshift occurs. The frameshift region consists of a heptanucleotide "slippery" sequence, 5′-UUUAAAC-3′, followed by a putative pseudoknot. ORF 1b encodes a protein of 155.4 kDa containing, in its N-terminal portion, an RNA-dependent RNA polymerase and an RNA helicase domain separated by a Zn finger domain. Another domain of unknown function that is also conserved in coronaviruses and toroviruses is located at the C-terminus of the ORF 1b product. Three cleavage sites in the ORF 1a polyprotein and three in the ORF 1b polyprotein were predicted for the chymotrypsin-like protease and tentatively delimit the mature nonstructural proteins of LDV. Six small, overlapping 3′ ORFs (ORFs 2 through 7) encode proteins with calculated sizes of 25.8, 21.6, 19.8, 23.9, 18.9, and 12.3 kDa. ORF 7 encodes the virion nucleocapsid protein Vp-1, while ORF 6 encodes the nonglycosylated envelope protein Vp2. ORFs 5, 4, 3, and 2 each encode glycoproteins which may be virion envelope proteins. LDV is closely related to equine arteritis virus, Lelystad virus (LV), and simian hemorrhagic fever virus. These four viruses belong to a new group of positive-strand RNA viruses and are related to coronaviruses and toroviruses.