本研究通过对乙型脑炎活疫苗减毒过程中间株SA 12—1．7株进行全序列测定和分析，进一步了解乙脑活疫 苗减毒及其稳定性的分子机制。根据已发表的SA 14．2株及SAl4株的序列，设计6对重叠引物，涵括整个乙脑病 毒的基因组，通过RT—PCR扩增出SA 12．1．7株的各cDNA片段，分别克隆到pGEM．T载体，转化至TG1受体菌 中，挑取阳性克隆进行鉴定后测序。结果表明SA 12—1．7株基因组全序列长10976个核苷酸，从96到10394为一 个长开放读码框，编码3432个氨基酸。与野毒株SAl4和疫苗株SA 14—2的核苷酸序列和氨基酸序列相比，同源 性均在99％ 以上，突变位点分散于各个区域，E区有5个位点与疫苗株一致而与野毒株不同，3个位点与野毒株一 致而与疫苗株不同，推测与其容易产生回复突变、恢复毒力有关。此外，NS3、NS5和3 NTR的几个位点可能与病 毒毒力稳定性相关。综上所述，乙脑病毒减毒中间株的基因组全序列基本类似于已发表的序列，若干突变位点影 响病毒的弱毒性及毒力的稳定性。全序列的测定对于研究疫苗株的减毒机理具有重要意义。

To sequence the full length genome of Japanese encephalitis virus attenuated strain SA14—12— 1—7．direct information about the genomic structure and the possible relationship to the attenuated and stability m echanism has been provided in this study．Six pairs of prim ers were designed according tO the published sequences of SA14—14—2 and SA14 strains，covering full—length genome of the JEV virus．Using RT—PCR，cDN A fragm ents Of SA14—12—1—7 strain were got and cloned into pGEM —T vector，then trans— formed into com petent TG1 hosts．The positive colones were screened and then the inserted fragm ents were sequenced．The results of sequence analysis show ed that genom e of SA14—12—1—7 strain consistes of 10976 nucleotides and containes a single open reading frame of 10299 nt which encodes a polyprotein of 3432 am ino acids．Com pared with the published sequence of SA14—14—2 and SA 14 strain，the hom ology of the nucleotide sequence and deduced am ino acid sequence were all more than 99％ ．the mutation sites were located in different regions．In E region，5 sites are the same as SA14—14—2 and other 3 sites are the same as SA14 strain．Some sites in NS3，NS5 and 3’NTR m ay relate w ith the attenuated stability．So the sequence of SA14—12—1—7 strain genome is sim ilar tO the published inform ation，several mutation sites are responsibe for the attenuation Of the virus and the virulence stability．The sequence analysis would aid in understanding attenuated mechanism of the vaccine．