Li J P, Bestwick R K, Spiro C, Kabat D
J Virol. 1987 Sep;61(9):2782-92. doi: 10.1128/JVI.61.9.2782-2792.1987.
The leukemogenic membrane glycoprotein of Friend spleen focus-forming virus (SFFV) has an apparent Mr of 55,000 (gp55), is encoded by a recombinant env gene, and occurs on cell surfaces and in intracellular organelles. There is evidence that the amino-terminal region of gp55 forms a dualtropic-specific domain that is connected to the remainder of the glycoprotein by a proline-rich linker (C. Machida, R. Bestwick, B. Boswell, and D. Kabat, Virology 144:158-172, 1985). Using the colinear form of a cloned polycythemic strain of SFFV proviral DNA, we constructed seven in-phase env mutants by insertion of linkers and by a deletion. The mutagenized SFFVs were transfected into fibroblasts and were rescued by superinfection with a helper murine leukemia virus. Four of the mutants cause erythroblastosis. These include one with a 6-base-pair (bp) insert in the ecotropic-related sequence near the 3' end of the gene, two with a 12- or 18-bp insert in the region that encodes the proline-rich linker, and one with a 6-bp insert in the dualtropic-specific region. The other mutants (RI, Sm1, and Sm2) are nonpathogenic and contain lesions in dualtropic-specific region. The other mutants (RI, Sm1, and Sm2) are nonpathogenic and contain lesions in dualtropic-specific sequences that are highly conserved among strains of SFFV. A pathogenic revertant (RI-rev) was isolated from one mouse that developed erythroblastosis 3 weeks after infection with RI. RI-rev contains a second-site env mutation that affects the same domain as the primary mutation does and that increases the size of the encoded glycoprotein. All pathogenic SFFVs encode glycoproteins that are expressed on cell surfaces, whereas the nonpathogenic glycoproteins are exclusively intracellular. The pathogenic SFFVs also specifically cause a weak interference to superinfection by dualtropic MuLVs. These results are compatible with the multidomain model for the structure of gp55 and suggest that processing of gp55 to plasma membranes is required for pathogenesis. The amino-terminal region of gp55 binds to dualtropic murine leukemia virus receptors, and this interaction is preserved in the SFFV mutants that cause erythroblastosis.
弗瑞德脾集落形成病毒（SFFV）的致白血病膜糖蛋白的表观分子量为55,000（gp55），由重组env基因编码，存在于细胞表面和细胞内细胞器中。有证据表明，gp55的氨基末端区域形成一个双嗜性特异性结构域，该结构域通过富含脯氨酸的连接子与糖蛋白的其余部分相连（C. 町田、R. 贝斯特威克、B. 博斯韦尔和D. 卡巴特，《病毒学》144:158 - 172，1985）。利用克隆的多血症性SFFV前病毒DNA的共线性形式，我们通过插入连接子和缺失构建了7个同相位env突变体。将诱变后的SFFV转染到成纤维细胞中，并用辅助性鼠白血病病毒进行超感染来拯救它们。其中4个突变体导致成红细胞增多症。这些突变体包括一个在基因3'端附近的嗜亲性相关序列中有6个碱基对（bp）插入的突变体，两个在编码富含脯氨酸连接子的区域中有12或18 bp插入的突变体，以及一个在双嗜性特异性区域中有6 bp插入的突变体。其他突变体（RI、Sm1和Sm2）无致病性，且在双嗜性特异性区域有损伤。其他突变体（RI、Sm1和Sm2）无致病性，且在SFFV毒株中高度保守的双嗜性特异性序列中有损伤。从一只在感染RI 3周后发生成红细胞增多症的小鼠中分离出一个致病性回复突变体（RI - rev）。RI - rev包含一个第二位点env突变，该突变影响与原发突变相同的结构域，并增加了编码糖蛋白的大小。所有致病性SFFV都编码在细胞表面表达的糖蛋白，而非致病性糖蛋白仅存在于细胞内。致病性SFFV还对双嗜性MuLV的超感染产生特异性的弱干扰。这些结果与gp55结构的多结构域模型相符，并表明gp55向质膜的加工对于发病机制是必需的。gp55的氨基末端区域与双嗜性鼠白血病病毒受体结合，并且这种相互作用在导致成红细胞增多症的SFFV突变体中得以保留。
