The sequences of the 3′-terminal 3.7 kb of the genome and of a 1.7 kb 5′ end cDNA clone of one isolate of lactate dehydrogenase-elevating virus (LDV) are reported. The 3′ end sequence encodes six major independent open reading frames (ORFs 2 to 7), which are overlapping by between one and 130 nucleotides. Each ORF is expressed at the 5′ end of one of six 3′-coterminal subgenomic mRNAs (mRNAs 2 to 7, respectively; 3.5 to 0.8 kb). The smallest mRNA, mRNA 7, encodes the nucleocapsid protein, VP1; mRNA 6 probably encodes the non-glycosylated envelope protein, VP2; and mRNAs 2 to 5 encode proteins of 26.0K, 21.5K, 19.2K and 22.4K, respectively, each possessing several potential -glycosylation sites and membrane-spanning segments. About 72% of the LDV genome segment carrying ORFs 2 to 7 exhibits about 50% or higher nucleotide identity with the corresponding genome segment of swine infertility and respiratory syndrome (Lelystad) virus (LV), whereas only limited similarity is observed in discontinuous regions of the same corresponding genome segments of LDV and equine arteritis virus (EAV). EAV and LV belong to the same new group of positive-strand RNA viruses as LDV. One additional subgenomic mRNA of about 4 kb is produced in LDV-but not in EAV- or LV-infected cells. The 5′ end of this mRNA (1-1) carries a continuous coding sequence. The N-terminal 80 amino acids of the predicted product exhibit about 50% identity with segments in the ORF 1b proteins of both EAV and LV. These segments are located 117 to 150 amino acids upstream of the C termini of the ORF 1b proteins of these viruses. The 5′ end cDNA clone contains part of a 5′ leader associated with all seven subgenomic mRNAs and the 5′ end of ORF 1a. The junctions between the 5′ leader and the bodies of all seven subgenomic mRNAs have been determined. Only a single junction sequence was detected for each mRNA. Linkage occurs between a 5′ UAUAACC 3′ sequence at the 3′ end of the leader and only partially identical segments specified down-stream in the genome preceding ORFs 2 to 7. The generated junctions differ for different subgenomic mRNAs but possess the consensus sequence 5′ U A CC 3′. In mRNA 7, the UA in positions 1 and 2 are derived from the leader, but a G in position 2 in mRNAs 1-1, 3 and 4 and an A in position 3 in mRNA 6 seem to be specified by the 3′ genomic sequences. Thus, the formation of these junctions is difficult to explain by a leader-primed mode of synthesis such as postulated for coronaviruses.


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