NUCLEOTIDE-SEQUENCE OF SWEET CLOVER NECROTIC MOSAIC DIANTHOVIRUS RNA-1

The complete nucleotide sequence of sweet clover necrotic mosaic diant hovirus (SCNMV) RNA-1 has been determined. RNA-1 consists of 3876 nucl eotides in length, containing three large open reading frames (ORFs). The 5'-proximal, internal and 3'-terminal ORFs potentially encode 27-k Da, 57-kDa and 37-kDa proteins, respectively. The frameshift event bet ween the C-terminus of the 27-kDa protein and extension of the N-termi nus of the 57-kDa protein may result in the formation of a 88-kDa prot ein which is presumed to be a replicase. The 37-kDa coat protein ORF i s located immediately downstream of the 57-kDa ORF. The same genome or ganization and high similarity (80-92%) of both the nucleotide sequenc es and the deduced amino acid sequences between red clover necrotic mo saic dianthovirus and SCNMV suggest that they originate from a common progenitor, but have divergent evolution later. Striking similarity wa s detected between the putative RNA-dependent RNA polymerase of SCNMV and that of the tombus-, carmo-, necro-, machlomo- and luteoviruses, s upporting a proposal that they belong to the same virus supergroup alt hough there is a relatively low degree of coat protein sequence simila rity in these viruses.