Sequence Analysis of the NS Gene of an NS Mutant of Influenza B Virus.

通过流感病毒A/Aichi/2/68与野生型B/Yamagata/1/73的反复回交，我们分离了一个B型病毒突变体，克隆201，其NS基因（RNA片段8）中携带突变。克隆201在MDCK细胞和受精卵中均能高效生长，并在感染后早期诱导MDCK细胞产生严重的细胞病变，经重配实验证实这是由于克隆201的NS基因突变所致。并且，由于移码到下游，翻译<NS_1>终止于425位，产生<NS_1>由127个氨基酸组成的多肽，比<NS_1>野生型B/Yamagata（281个氨基酸）短一半以上。除缺失外，还观察到10个点突变，包括4个沉默突变。测序数据与以下发现一致：201的RNA片段8在聚丙烯酰胺凝胶中的迁移略快于野生型对应物，201缺少<NS_1>B/Yamagata（分子量39，800）的蛋白条带，而在B/<NS_2>Yamagata（分子量19，000）的位置处存在重条带。克隆201诱导的严重细胞溶解是否是由于大羧基末端缺失<NS_1>或点突变所致尚待确定。

By repeated back-crosses of influenza virus A/Aichi/2/68 with wild type B/Yamagata/1/73, we isolated a B type virus mutant, clone 201, bearing mutations in the NS gene ( RNA segment 8 ). Clone 201 grew efficiently both in MDCK cells and in fertile hens' eggs, and induced a severe cytopathic effect in MDCK cells early after infection, which was ascribed to the function of the mutated NS gene of clone 201 by reassortment experiment.Sequencing analysis of the NS gene of clone 201 revealed that there is a deletion of 13 bases from position 374 - 386 of the plus sense RNA, and, due to the frame shift downstream, the translation of <NS_1> stops at position 425, giving rise to an <NS_1> polypeptide consisting of 127 amino acids, more than a half shorter than the <NS_1> of wild type B/Yamagata ( 281 amino acids ). In addition to the deletion, 10 point mutations were noticed, including 4 silent mutations.The sequencing data are consisting with the findings that RNA segment 8 of 201 migrates slightly faster than the wild type counterpart in the polyacrylamide gel, and that 201 lacks the protein band for the <NS_1> of B/Yamagata ( Molecular Weight 39,800 ) and a heavy band is present instead at the position of <NS_2> of B/Yamagata ( Molecular Weight 19,000 ).Whether severe cytolysis induced by clone 201 is due to the large carboxy terminal deletion of <NS_1> or to the point mutation(s) is yet to be determined.