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 thre e RNA species (6.5, 3.0 and 2.5 kb). Hybridization tests with cloned c DNA probes showed that none of these species was derived from another. RNA 2 (2962 nt), which was sequenced, has non-coding regions of 368 n t and 285 nt at the 5' end and 3' end, respectively. Near the 5' termi nus, 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 nucle otide. From the 5' end, the four open reading frames encode proteins o f 51K, 13K, 21K and 8K. The first three of these have sequence similar ity to the triple-gene-block proteins of other viruses, particularly b arley stripe mosaic hordeivirus. The 51K protein contains a putative N TP-binding motif and the 13K and 21K proteins each contain two hydroph obic regions separated by a hydrophilic region. The 8K protein is rich in cysteine. PMTV differs from other furoviruses in having a triparti te genome. Its RNA 2 differs in gene content from the RNA 2 of soil-bo rne 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.