Sequence Analysis and GTP-Binding Ability of the Minor Core Protein P5 of Rice Gall Dwarf Virus

Analysis of the nucleotide sequence of the genome segment S5 of Rice gall dwarf virus (RGDV), which belongs to the genus Phytoreovirus, revealed that this segment encodes a putative protein of approximately 91 kDa. Antiserum raised against the protein reacted with a minor structural protein of similar size in RGDV, demonstrating that S5 encodes the structural protein of RGDV. The protein named P5 appeared to be a component of viral core particles. Although no overall homology was found to any other proteins, including those of animal-infecting reoviruses, P5 of RGDV exhibited a significant homology to P5 of Rice dwarf virus (50%), which might be a guanylyltransferase, and to P5 of Wound tumor virus (55%). These results, together with the observation that P5 bound guanosine triphosphate suggest that P5 of RGDV shows a guanylyltransferase activity and, moreover, that plant-infecting reoviruses have a similar functional and/or structural organization to that of animal-infecting reoviruses.