RICE RAGGED STUNT ORYZAVIRUS GENOME SEGMENTS S7 AND S10 ENCODE NONSTRUCTURAL PROTEINS OF M-R 68-025 (PNS7)AND M-R 32-364 (PNS10)

The nucleotide sequences of genome segments S7 and S10 of a Thai-isola te of rice ragged stunt virus (RRSV) were determined. The 1 938 bp S7 sequence contains a single large open reading frame (ORF) spanning nuc leotides 20 to 1 843 that is predicted to encode a protein of M-r 68 0 25. The 1 162 bp S10 sequence has a major ORF spanning nucleotides 142 to 1 032 that is predicted to encode a protein of M-r 32 364. This S1 0 ORF is preceded by a small ORF (nt 20-55) which is probably a minici stron. Coupled in vitro transcription-translation from the two major O RFs gave protein products of the expected sizes. However, no protein w as visualised from S10 when the small ORF sequence was included. Prote ins were expressed in Escherichia coli from the full length ORF of S7 (P7) and from a segment of the S10 ORF (P10) fused to the ORF of gluta thione S-transferase (GST). Neither fusion protein was recognised by p olyclonal antibodies raised against RRSV particles. Furthermore, polyc lonal antibodies raised against GST-P7 fusion protein did not recognis e any virion structural polypeptides. These data strongly suggest that the proteins P7 and P10 do not form part of RRSV particle. This is fu rther supported by observed sequence homology (though very weak) of pr edicted RRSV P7 and P10 with those of rice dwarf virus (RDV) non-struc tural proteins Pns6 and Pns9, respectively.