The 3'terminus of lactate dehydrogenase-elevating virus genome RNA does not contain togavirus or flavivirus conserved sequences

Lactate dehydrogenase-elevating virus (LDV): subgenomic mRNAs, mRNA leader and comparison of 3'-terminal sequences of two LDV isolates

The 3'-terminal 1314 nucleotides of the genome of one isolate of lactate dehydrogenase-elevating virus, LDV-P, has been derived by sequence analyses of cDNAs from several genomic libraries and compared to that of another LDV isolate, LDV-C (Godeny et al. (1990) Virol. 177, 768-771). The 3'-non-coding segment of 80 nucleotides of the two LDV genomes is identical, whereas marked, but varying nucleotide and amino acid divergence is apparent in the three upstream overlapping open reading frames (ORF). The third ORF from the 3'-end exhibits only 82% nucleotide and 90% amino acid identity, whereas the 3'-terminal ORF, which encodes the nucleocapsid protein, exhibits approximately 99% amino acid identity. The second 3'-terminal ORF encodes an 18.8 kDa protein which lacks N-glycosylation sites but possesses 2 or 3 potential transmembrane helices in the N-terminal half of the molecule. A similar membrane organization is observed for the corresponding protein of equine arteritis virus and the M protein of mouse hepatitis virus. The sequence analyses combined with Northern hybridization analyses of RNA from LDV-infected macrophages and spleens of LDV-infected mice indicate that the three ORFs encoded by the 3'-terminal end of the LDV genome are expressed via the three smallest mRNAs (mRNAs 6-8) of the seven subgenomic mRNAs of LDV (mRNAs 2-8), which range in size from about 0.8 to 3.6 kb. All mRNAs have been shown to carry poly(A)-tracts and a common leader sequence. The seven mRNAs were produced in infected macrophage cultures concomitantly with genomic LDV RNA. Maximum LDV RNA synthesis was observed between 6 and 8 h post-infection. The same seven subgenomic mRNAs were detected in macrophages infected with three different isolates of LDV, but different relative amounts of some of the mRNAs were produced. The relative proportions of molecules of mRNAs 1-8 present in 6 h LDV-P-infected macrophages were about 13, 5, 5, 8, 6, 11, 11 and 27% of the total, respectively.

Lactate dehydrogenase-elevating virus, equine arteritis virus, and simian hemorrhagic fever virus: a new group of positive-strand RNA viruses

The last comprehensive reviews of nonarbotogaviruses included discussions on pestiviruses, rubella virus, lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV), simian hemorrhagic fever virus (SHFV), cell fusion agent, and nonarboflaviviruses. The inclusion of all these viruses in the family Togaviridae was largely based on the similarities in morphological and physical–chemical properties of these viruses, and in the sizes and polarities of their genomes. In the intervening years, considerable new information on the replication strategies of these viruses and the structure and organization of their genomes has become available that has led to the reclassification or suggestions for reclassification of some of them. The replication strategy of EAV resembles that of the coronaviruses, involving a 3'-coterminal nested set of mRNAs. Therefore, EAV has been suggested to be included in a virus superfamily, along with coronaviruses and toroviruses. Recent evidence indicates that LDV not only resembles EAV in morphology, virion and genome size, and number and size of their structural proteins, but also in genome organization and replication via a 3'-coterminal set of mRNAs. SHFV, although not fully characterized, exhibits properties resembling those of LDV and EAV, and the recent evidence suggest that it may possess the same genome organization as these viruses. The three viruses may, therefore, represent a new family of positive-strand RNA viruses and are reviewed together in this chapter. In this chapter, emphasis is on the recent information concerning their molecular properties and pathogenesis in vitro and in vivo and on the host immune responses to infections by these viruses.

A nested set of eight RNAs is formed in macrophages infected with lactate dehydrogenase-elevating virus

Total RNA was extracted from primary cultures of mouse macrophages isolated from 10-day-old mice 6 to 12 h postinfection with lactate dehydrogenase-elevating virus (LDV). Poly(A)+ RNA was extracted from spleens of 18-h LDV-infected mice. The RNAs were analyzed by Northern (RNA) blot hybridization with a number of LDV-specific cDNAs as probes. A cDNA representing the nucleocapsid protein (VP-1) gene located at the 3' terminus of the viral genome (E. K. Godeny, D. W. Speicher, and M. A. Brinton, Virology 177:768-771, 1990) hybridized to viral genomic RNA of about 13 kb plus seven subgenomic RNAs ranging in size from about 1 to about 3.6 kb. Two other cDNA clones hybridized only to the four or five largest subgenomic RNAs, respectively. In contrast, two cDNAs encoding continuous open reading frames with replicase and zinc finger motifs hybridized only to the genomic RNA. The replicase motif exhibited 75% amino acid identity to that of the 1b protein of equine arteritis virus (EAV) and 44% amino acid identity to those of the 1b proteins of coronaviruses and Berne virus. Combined, the results indicate that LDV replication involves formation of a 3'-coterminal-nested set of mRNAs as observed for coronaviruses and toroviruses as well as for EAV, with which LDV shares many other properties. Overall, LDV, like EAV, possesses a genome organization resembling that of the coronaviruses and toroviruses. However, EAV and LDV differ from the latter in the size of their genomes, virion size and structure, nature of the structural proteins, and symmetry of the nucleocapsids.

Map location of lactate dehydrogenase-elevating virus (LDV) capsid protein (Vp1) gene

Lactate dehydrogenase-elevating virus (LDV) is currently classified within the Togaviridae family. In an effort to obtain further information on the characteristics of this virus, we have begun to sequence the viral RNA genome and to map the virion structural protein genes. A sequence of 1064 nucleotides, which represents the 3' terminal end of the genome, was obtained from LDV cDNA clones. A 3' noncoding region of 80 nucleotides followed by two complete open reading frames (ORFs) were found within this sequence. The two ORFs were in different reading frames and overlapped each other by 11 nucleotides. One ORF encoded a protein of 170 amino acids and the other ORF, located adjacent to the 3' noncoding region of the viral genome, encoded a 114 amino acid protein. Thirty-three N-terminal residues were sequenced directly from purified LDV capsid protein, Vp1, and this amino acid sequence mapped to the ORF adjacent to the 3' noncoding region. The presence of overlapping ORFs and the 3' terminal map position of Vp1 indicate that LDV differs significantly from the prototype alpha togaviruses.