Shahrabadi M S, Babiuk L A, Lee P W
Virology. 1987 May;158(1):103-11. doi: 10.1016/0042-6822(87)90242-x.
Previously we reported that calcium plays an important role in the maturation of bovine rotavirus (M. S. Shahrabadi and P. W. K. Lee, 1986. Virology 152, 298-307). We now demonstrate that the formation of mature double-shelled (L) particles was strictly dependent on the concentration of calcium present in the growth medium. The formation of single-shelled (D) particles did not appear to be a calcium-mediated process. Subsequent labeling studies using 45Ca revealed that calcium was incorporated into the L particles but not the D particles. The previously noted decreased level of the outer capsid protein VP7 (42K) in calcium-deprived cultures was now found to be due to the preferential degradation, and not to the impaired synthesis, of this protein in the absence of calcium. It was further demonstrated that calcium had a stabilizing effect on VP7 and that VP7 synthesized in the presence of calcium was not degraded upon subsequent calcium deprivation. Protein degradation during calcium deprivation was apparently limited to the mature form of VP7 since the unglycosylated precursor (pVP7), formed in the presence of tunicamycin, was found to be stable under this condition. Electron microscopic examination of infected cells revealed that in the presence of calcium, virus maturation took place by the budding of viral cores through the endoplasmic reticulum (ER). No such budding was observed in calcium-deprived cells. In these cells mature virions were absent and membrane fragments could be found associated with viral cores or single-shelled particles.
此前我们报道过钙在牛轮状病毒成熟过程中起重要作用（M. S. 沙赫拉巴迪和P. W. K. 李，1986年。《病毒学》152卷，298 - 307页）。我们现在证明成熟双层（L）颗粒的形成严格依赖于生长培养基中钙的浓度。单层（D）颗粒的形成似乎不是一个由钙介导的过程。随后使用45Ca进行的标记研究表明，钙被整合到L颗粒中，而不是D颗粒中。现在发现，之前提到的在缺钙培养物中外衣壳蛋白VP7（42K）水平降低是由于在没有钙的情况下该蛋白被优先降解，而不是合成受损。进一步证明钙对VP7有稳定作用，并且在有钙存在的情况下合成的VP7在随后缺钙时不会被降解。缺钙期间的蛋白质降解显然仅限于VP7的成熟形式，因为在衣霉素存在下形成的未糖基化前体（pVP7）在这种条件下被发现是稳定的。对感染细胞的电子显微镜检查显示，在有钙的情况下，病毒成熟通过病毒核心通过内质网（ER）出芽发生。在缺钙细胞中未观察到这种出芽。在这些细胞中没有成熟的病毒粒子，并且可以发现膜碎片与病毒核心或单层颗粒相关。
