VIRAL POLYPEPTIDES AND RNA OF DEFECTIVE INTERFERING PARTICLES OF IPN VIRUS GENERATED BY SERIAL UNDILUTED PASSAGING IN TO-2 CELLS

HB-1 virus, a strain of infectious pancreatic necrosis virus (IPNV), was isolated from hard clam, Meretrix lusoria, with TO-2 cell line derived from tilapia ovary. The defective interfering (DI) particles of HB-1 virus could be generated by serial undiluted passaging. The polypeptides and RNA in virus particles of diluted and undiluted virus preparations were compared in order to investigate the nature of defective interfering particles involved in viral interference of HB-1 virus. Cesium chloride density gradient centrifugation was applied to purify virus particles of diluted and undiluted virus preparations. By comparing the polypeptides and RNA in virus particles of diluted and undiluted virus preparations, it was revealed that (I) the virus particles of undiluted virus preparation had smaller beta-polypeptides than normal; (II) subgenomic RNA of large segment was found in virus particles of undiluted virus preparation. These two findings suggested that DI particles of HB-1 virus was a deletion mutant of standard virus. This is the first report indicating the polypeptides and RNA possibly related to IPN virus DI particles.