Nucleotide sequence and genomic organization of melon necrotic spot virus

1 Department of Plant Science, University of British Columbia, Vancouver, British Columbia V6T 2A2 and 2 Research Station, Agriculture Canada, 6660 N.W. Marine Drive, Vancouver, British Columbia, Canada V6T 1X2 Cloned cDNA copies of the genomic RNA of melon necrotic spot virus (MNSV) have been sequenced and the sizes and locations of predicted viral proteins have been deduced. The genome consists of at least 4262 nucleotides and the positive strand contains three to five open reading frames (ORFs) which may be expressed. The 5' proximal ORF encodes a 29K protein (p29) and terminates with an amber codon which may be read through to produce an 89K protein (p89). Two small centrally located ORFs each encode a 7K protein (p7A and p7B). As p7A is in frame with p7B, readthrough of the amber codon terminating p7A may occur, producing a 14K protein (p14). The 3' proximal ORF encodes the 42K coat protein. The genomic organization of MNSV, its probable translation strategy and the amino acid sequences of its putative proteins closely resemble those of known carmoviruses, suggesting that MNSV should be classified as a member of the carmovirus group. Unusual properties of the putative MNSV replicase (p89) suggest that MNSV should be classified in a new virus supergroup with several other viruses sharing these properties. Received 20 December 1989; accepted 10 May 1990.