Summary auto-generated
Researchers identified Nicotiana velutina mosaic virus (NVMV) as having a bipartite genome consisting of two distinct RNA molecules of approximately 8 kb and 3 kb in size. By cloning NVMV RNA and using Northern blot hybridization analysis with selected DNA probes, they confirmed these two non-homologous RNA components in purified virus and infected plant tissue. Sequencing approximately 75% of the 3 kb RNA 2 revealed four open reading frames (ORFs) encoding proteins of 20K, 39K, 13K, and an incomplete 9K protein. Notably, three of these ORFs overlapped in a triple gene block arrangement similar to that found in beet necrotic yellow vein virus, barley stripe mosaic virus, and potato viruses X and M. Amino acid comparisons revealed significant homologies between NVMV proteins and those of related viruses, particularly an NTP-binding motif and viral DNA polymerase domain in the 39K protein. Although the bipartite genome and gene organization suggest affinities with furoviruses, NVMV shows unique biological properties and lacks serological relationships with known virus groups, suggesting it may represent a distinct taxonomic position.
Key findings
- NVMV has a bipartite genome comprising an 8 kb RNA 1 and a 3 kb RNA 2, identified through molecular cloning and Northern blot analysis
- NVMV RNA 2 contains a triple gene block (ORFs 2, 3, and 4) with overlapping arrangement similar to furoviruses and related viruses
- The 39K protein product contains conserved motifs for NTP-binding and viral DNA polymerase activity, suggesting a role in viral replication
- Particle morphology and RNA sizes suggest similarities to furoviruses, but unique biological properties and lack of serological cross-reactivity indicate NVMV has no clear taxonomic relationship to established virus groups
- About 75% of RNA 2 sequence was determined, revealing conserved amino acid homologies with BNYVV, BSMV, and potato virus proteins
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Abstract
DNA complementary to Nicotiana velutina mosaic virus (NVMV) RNA was cloned and five segments larger than 0.9 kb were used in Northern blot hybridization analysis to identify two virus-specific RNAs, approximately 8 kb (RNA 1) and 3 kb (RNA 2) in size. The clones selected as probes did not hybridize with RNA from various tobamoviruses, or from beet necrotic yellow vein (BNYVV) and peanut clump furoviruses. In an attempt to determine the taxonomic position of the virus, about 75% of the NVMV RNA 2 was sequenced and four open reading frames (ORFs) were identified. ORFs 1, 2 and 3 encode proteins of Mr 20K, 39K and 13K, whereas ORF 4 was incomplete. ORFs 2, 3 and 4 overlapped in an arrangement closely resembling the triple gene block identified in BNYVV RNA 2, barley stripe mosaic virus (BSMV) RNA 2, potato virus X and potato virus M RNA. The presumed coat protein gene of NVMV RNA 2 (ORF 1) is situated to the 5' side of the triple gene block as for BNYVV and BSMV RNA 2. Amino acid homologies were dtected among the 13K and 14K proteins of NVMV RNA 2, BNYVV RNA 2 and BSMV RNA 2. Significant homology was also detected between the 39K protein of NVMV RNA 2 and the 42K protein of BNYVV RNA 2, with a motif specific for ATP- and GTP-binding (NTP-binding motif), and a conserved viral DNA polymerase domain. The presence of a triple gene block in NVMV RNA 2 indicates that NVMV has affinities with members of the hordei-, furo-, potex- and carlavirus groups but not with the tobamovirus group. The divided RNA genome of NVMV, and the sizes of the two RNAs suggest that NVMV is most closely allied to the furoviruses, but the unique nature of its different biological properties and lack of any serological relationships with furoviruses lead us to conclude that NVMV has no clear relatedness to any taxonomic group of plant viruses.