Yoshikura H, Tejima S
Virology. 1981 Sep;113(2):503-11. doi: 10.1016/0042-6822(81)90178-1.
A plaque mutant was isolated from Kirsten mouse sarcoma virus-transformed BALB/c cells persistently infected with a mouse hepatitis virus strain MHV-S. While the wild type produced large plaques consisting of fused cells (fusion type) both at 39 and at 32°, the mutant produced small fusion-type plaques at 39°, and at 32°, only after longer incubation, plaques consisting of round dead cells (non-fusion type) were obtained. The mutant grew equally well at both temperatures. Thus, the mutant was cold sensitive in inducing cell fusion, but not in replication or in ultimate cell killing. The cold sensitivity was overcome by the addition of trypsin (0.04 to 0.05%) to the culture medium, but not by treating the virions with trypsin. SDS-polyacrylamide gel electrophoresis of the virion proteins failed to detect differences between the wild type and the mutant. In intracellular viral proteins immunoprecipitated with anti-MHV-S rabbit serum, a protein of 68,000 daltons (68K protein) which was present in the wild type-infected cells was absent in the mutant-infected cells, but trypsin treatment or incubation at 39° of the mutant-infected cells failed to induce the 68K protein. After six to seven undiluted passages, the mutant segregated varieties of mutants which were partially or totally reverted to the wild type in phenotype, and also those whose cell fusion induction was absent even at 39°. All these mutants failed to induce the 68K protein in the infected cells. Thus, there was no linkage between the presence of 68K protein and the fusion induction. Trypsin treatment of the infected cells enabled MHV-S to form fusion plaques on otherwise resistant cells, and MHV-2, a producer of non-fusion-type plaques, to form fusion-type plaques. Protease appears to play an important role in MHV-induced cell fusion in general.
从持续感染小鼠肝炎病毒株MHV - S的 Kirsten 小鼠肉瘤病毒转化的 BALB/c 细胞中分离出一个噬斑突变体。野生型在39°和32°时都产生由融合细胞组成的大噬斑（融合型），而该突变体在39°时产生小的融合型噬斑，在32°时，仅在更长时间培养后，才获得由圆形死细胞组成的噬斑（非融合型）。该突变体在这两种温度下生长同样良好。因此，该突变体在诱导细胞融合方面对温度敏感，但在复制或最终细胞杀伤方面不敏感。通过向培养基中添加胰蛋白酶（0.04%至0.05%）可克服这种冷敏感性，但用胰蛋白酶处理病毒粒子则不能。病毒粒子蛋白的 SDS - 聚丙烯酰胺凝胶电泳未能检测到野生型和突变体之间的差异。在用抗MHV - S兔血清免疫沉淀的细胞内病毒蛋白中，野生型感染细胞中存在的一种68,000道尔顿的蛋白（68K蛋白）在突变体感染细胞中不存在，但对突变体感染细胞进行胰蛋白酶处理或在39°孵育未能诱导出68K蛋白。经过六到七次未稀释传代后，该突变体分离出各种突变体，这些突变体在表型上部分或完全回复为野生型，还有一些即使在39°时也不诱导细胞融合。所有这些突变体在感染细胞中都不能诱导68K蛋白。因此，68K蛋白的存在与融合诱导之间没有联系。用胰蛋白酶处理感染细胞可使MHV - S在原本抗性的细胞上形成融合噬斑，也可使非融合型噬斑产生者MHV - 2形成融合型噬斑。一般来说，蛋白酶似乎在MHV诱导的细胞融合中起重要作用。
