The stability of E protein gene of the Japanese encephalitis live attenuated vaccine virus SA_(14)-14-2

The purpose of this study was to understand the stability and possibility of back mutation of Japanese encephalitis （JE） attenuated vaccine virus strain SA14-14-2 HK8 on molecular level. The E genes of the SA14-14-2 HK8 vaccine virus and its PHK cells passaged virus (SA14-14-2 HK17), its mouse brain passaged virus (SA14-14-2 SM1) were sequenced and compared with the E gene of parental SA14 virus. The total RNA was extracted from infected Vero cells and amplified by RT-PCR. The RT-PCR products were purified and cloned into T-vector. Positive clones were screened, identified and sequenced. There were twelve nucleotides and eight amino acids substitutions between SA14 parent virus and SA14-14-2 PHK8 vaccine virus. The SA14-14-2 PHK17 virus showed two additional mutations （E-331 and E-398） which were not back mutations. Although five additional mutations were found in SA14-14-2 SM1 virus, only one （E-107） was back mutation. Genetic characteristics of the attenuated vaccine virus SA14-14-2 were stable when it was passaged 17 times on PHK cells or one time in mouse brains.

The purpose of this study was to understand the stability and possibility of back mutation of Japanese encephalitis （JE） attenuated vaccine virus strain SA14-14-2 HKs on molecular level. The E genes of the SA14-14-2 HKs vaccine virus and its PHK cells passaged virus （SA14-14-2 HK17 ）, its mouse brain passaged virus （SA14-14-2 SM1 ） were sequenced and compared with the E gene of parental SAI4 virus. The total RNA was extracted from infected Vero cells and amplified by RT-PCR. The RT-PCR products were purified and cloned into T-vector. Positive clones were screened, identified and sequenced. There were twelve nucleotides and eight amino acids substitutions between SA14 parent virus and SA14-34-2 PHKs vaccine virus. The SA14-14-2 PHK17 virus showed two additional mutations （E-331 and E-398） which were not back mutations. Although five additional mutations were found in SA14-34-2 SMt virus, only one （E-307） was back mutation. Genetic characteristics of the attenuated vaccine virus SA14- 34-2 were stable when it was passaged 37 times on PHK cells or one time in mouse brains.