The nucleotide sequence of potato mop-top virus RNA 2: a novel type of genome organization for a furovirus.

Particles of isolate T of potato mop-top furovirus (PMTV) contain three RNA species (6.5, 3.0 and 2.5 kb). Hybridization tests with cloned cDNA probes showed that none of these species was derived from another. RNA 2 (2962 nt), which was sequenced, has non-coding regions of 368 nt and 285 nt at the 5' end and 3' end, respectively. Near the 5' terminus, nucleotides 46 to 110 are able to form a stem-loop structure, the stem of which has 23 bp with only one mismatch and one unpaired nucleotide. From the 5' end, the four open reading frames encode proteins of 51K, 13K, 21K and 8K. The first three of these have sequence similarity to the triple-gene-block proteins of other viruses, particularly barley stripe mosaic hordeivirus. The 51K protein contains a putative NTP-binding motif and the 13K and 21K proteins each contain two hydrophobic regions separated by a hydrophilic region. The 8K protein is rich in cysteine. PMTV differs from other furoviruses in having a tripartite genome. Its RNA 2 differs in gene content from the RNA 2 of soil-borne wheat mosaic virus, which lacks a triple gene block, and from that of beet necrotic yellow vein virus, which has a coat protein gene and read-through domain to the 5' side of its triple gene block. The gene arrangement in PMTV is therefore novel for a furovirus.