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The complete nucleotide sequence of rice dwarf phytoreovirus (RDV) genome segment S11 was deter-mined. S I 1 is 1067 nucleotides long. There is an inverted repeat of 10 bp adjacent o the conserved 5'-terminal hexanucleotide (5 ' GGUAAA 3') and 3'-terminal tetranucleotide (5 ' UAGU 3') sequences. A single large open reading frame found in the plus strand of $11 begins with the first AUG codon (bases 6 to 8) and extends for 567 bases. Evolutionary relatedness between RDV S11 and wound tumour phytoreovirus S12 based on amino acid sequence similarity (25.8%) was found. In addition to the first AUG triplet, RDV S 11 possesses a second in-phase AUG triplet (positions 30 to 32) nearby, which conforms to the Kozak consensus equence. Two forms of the protein were identified by using an in vitro transcription and translation system in which a tailored full-length cDNA was the initial template. The abolition of the first AUG codon by site-directed mutagenesis resulted in disappearance of the larger translation product. These results trongly suggest that the two products are translated from the first and second AUG codons. Whether the two proteins are expressed in vivo is at present unclear