Sequence analysis and genome organisation of poinsettia mosaic virus (PnMV) reveal closer relationship to marafiviruses than to tymoviruses

Sequence comparison and genome organisation of poinsettia mosaic virus (PnM V), a putative member of the tymoviruses, revealed a closer relationship to marafiviruses. The complete nucleotide sequence of PnMV was determined. Th e 6099-nt RNA genome encodes a putative 221-kDa polyprotein that lacks a st op codon between the replicase and the coat protein genes, as in most tymov irus RNAs. The genomic RNA has a poly(A) tail at its 3'-terminus in contras t to the tRNA-like structure found in the RNA of most tymoviruses, and no h omology was observed to the conserved noncoding region of the tymoviral 3'- termini. The tymobox of PnMV, a 16-nt region of the subgenomic RNA (sgRNA) promoter shared by most tymoviruses, differs in 3 nt from the RNA sequence of tymoviruses but is identical to the sequence of marafiviruses. At least three sgRNAs were found in PnMV-infected Euphorbia pulcherrima and in isola ted PnMV particles; one that is 650 nt long encodes the 21.4-kDa coat prote in, and the others are about 3.5 and 1.7 kb and contain the 5'- and the 3'- terminal parts of genomic RNA, respectively. Like tymoviruses, PnMV particl es sediment as top and bottom components. The particles of the top componen t contain the sgRNA (650 nt) encoding the coat protein, and those of bottom component contain both genomic and sgRNAs. (C) 2000 Academic Press.