Ozers M S, Friesen P D
Institute for Molecular Virology, Graduate School and College of Agricultural and Life Sciences, University of Wisconsin at Madison 53706, USA.
Virology. 1996 Dec 15;226(2):252-9. doi: 10.1006/viro.1996.0653.
TED is a 7.5-kbp member of the gypsy family of retrotransposons that was first identified by its integration within the baculovirus DNA genome. This lepidopteran (moth) transposon contains three retrovirus-like genes, including functional gag and pol that yield reverse transcriptase-containing virus-like particles. To identify and characterize the product(s) of the third env-like open reading frame, TED ORF3 was expressed in homologous lepidopteran cells by using a baculovirus vector, vENV. Immunoblots and immunoprecipitations with antiserum raised against a bacterial ORF3-fusion protein detected two ORF3-encoded proteins, p68env and gp75env. On the basis of selective incorporation of [3H]mannose and inhibition of modification by tunicamycin which blocks N-linked glycosylation, gp75env is a glycoprotein derived from core precursor p68env. As predicted by the presence of a transmembrane domain near the carboxyl terminus, both p68env and gp75env were associated with heavy membranes of vENV-infected cells. Thus, TED ORF3 encodes a membrane glycoprotein with properties characteristic of retroviral env proteins. These data are consistent with the hypothesis that TED is an invertebrate retrovirus. Moreover, TED integration within the baculovirus genome provides an example of retroelement-mediated acquisition of host genes that may contribute to virus evolution.
TED是逆转录转座子吉普赛家族的一个7.5千碱基对成员，最初是因其整合进杆状病毒DNA基因组而被鉴定出来的。这种鳞翅目（蛾类）转座子包含三个逆转录病毒样基因，包括功能性的gag和pol，它们能产生含有逆转录酶的病毒样颗粒。为了鉴定和表征第三个env样开放阅读框的产物，利用杆状病毒载体vENV在同源鳞翅目细胞中表达了TED ORF3。用针对细菌ORF3融合蛋白产生的抗血清进行免疫印迹和免疫沉淀，检测到两种由ORF3编码的蛋白，即p68env和gp75env。基于[3H]甘露糖的选择性掺入以及衣霉素（它能阻断N-连接糖基化）对修饰的抑制作用，gp75env是一种源自核心前体p68env的糖蛋白。正如羧基末端附近存在跨膜结构域所预测的那样，p68env和gp75env都与vENV感染细胞的重膜相关。因此，TED ORF3编码一种具有逆转录病毒env蛋白特征的膜糖蛋白。这些数据与TED是一种无脊椎动物逆转录病毒的假说相一致。此外，TED整合进杆状病毒基因组提供了一个逆转元件介导宿主基因获得的例子，这可能有助于病毒进化。
