The complete nucleotide sequence of rice dwarf virus (RDV) genome segment 4 was determined. Genome segment 4 was 2468 nucleotides long and had a long open reading frame initiating at nucleotides 64 to 66 and terminating at 2245 to 2247. The deduced polypeptide contained 727 amino acid residues with an Mr of 79.8K. Amino acid sequences similar to a 'zinc-finger' and purine NTP-binding motifs were present in the deduced polypeptide. Considerable amino acid sequence homology was detected between genome segment 4 of RDV and wound tumor virus (WTV). One of the sequences similar to the 'zinc-finger' motif was present in a conserved region of the polypeptide of both viruses. However, the sequence similar to the purine NTP-binding motif was not present in the polypeptide encoded by genome segment 4 of WTV.