Structure and Function of Genes Involved in Insect Transmission of Rice Ragged Stunt Virus.

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1) When the genomic dsRNAs were electrophoresed, two types of genome segment 9 (S9) were detected by the mobility shift.The faster and slower migrating bands were designated as L and U,respectively.Although most of the isoates with L were not transmitted efficiently, some were in the same efficiency as those with U.2) cDNAs to U and L were synthesized from the genomic dsRNAs, cloned into a plasmid vector pUC119, and sequenced.Both had the same length of 1132 nucleotides, therefore the mobility shift was not due to the differencein in length.L had some substitutions compared with U and the A to C convertion at a nucleotide position of 843 was common in all Ls.In order to prove this convertion results in the mobility shift, synthetic U and L having different nucleotides only at the position 843 were made.The electrophoretic analysis showed the convertion is responsible to the mobility shift.The substitution created the Asp to Ala convertion of the encoded polypeptide.3) An isolate with L having an equal insect transmission rate was found to have another substitution at a nucleotide position 486 in addition to taht at the position 843.This change results in Asn to Ser convertion of the encoded polypeptide.4) A polypeptide encoded by S9 was expressed in E.coli and antisera to the protein was made.In western blotting analyzes using the antibodies to the protein, only 38.6 K polypeptide located on a virion surface reacted positively among five structual polypeptides.Above results indicated that 38.6K polypeptide located on the virion surface is involved in insect transmission interacting probably with receptors of an insect vector.