Tegtmeyer P, Rundell K, Collins J K
J Virol. 1977 Feb;21(2):647-57. doi: 10.1128/JVI.21.2.647-657.1977.
The A protein of simian virus 40 is phosphorylated in both productive and transforming infection. The phosphorylated amino acid has been identified as serine and has been localized in a single tryptic peptide of the protein. Because the A protein synthesized in infection by A mutants is phosphorylated to the same extent and in the same peptide as in infection by wild-type virus, the functional defect of the A mutants is apparently unrelated to phosphorylation. At least three distinct forms of the A protein with apparent molecular weights of 85,000, 88,000, and 100,000 can be identified in extracts of cells infected by wild-type virus. After exposure of cells to Nonidet P-40, the 85,000- and 88,000-dalton proteins were found in varying amounts in extracts of permissive cells but not in extracts of transformed cells. This finding raised the question of the possible functional importance of the smaller proteins in productive infection. However, the virtual absence of the 85,000- and 88,000-dalton proteins in some extracts of the fully permissive CV-1 cell line indicates that a conversion of the larger to the smaller forms of the A protein is not required in significant quantity for productive infection. Furthermore, a study of extraction conditions shows that the smaller proteins are easily generated during extraction and provides an explanation for the appearance of these proteins in some cells after extraction under unfavorable conditions.
猿猴病毒40的A蛋白在增殖性感染和转化性感染中都会发生磷酸化。已确定磷酸化的氨基酸为丝氨酸，且定位在该蛋白的一个胰蛋白酶肽段中。由于A突变体感染时合成的A蛋白与野生型病毒感染时一样，在相同肽段中以相同程度发生磷酸化，所以A突变体的功能缺陷显然与磷酸化无关。在野生型病毒感染的细胞提取物中，至少可以鉴定出三种表观分子量分别为85,000、88,000和100,000的不同形式的A蛋白。在用非离子型去污剂P - 40处理细胞后，在允许性细胞的提取物中发现了不同含量的85,000道尔顿和88,000道尔顿的蛋白，但在转化细胞的提取物中未发现。这一发现引发了关于较小蛋白在增殖性感染中可能的功能重要性的问题。然而，在完全允许性的CV - 1细胞系的一些提取物中几乎不存在85,000道尔顿和88,000道尔顿的蛋白，这表明在增殖性感染中，大量将较大形式的A蛋白转化为较小形式并非必需。此外，一项关于提取条件的研究表明，较小的蛋白在提取过程中很容易产生，这就解释了在不利条件下提取后这些蛋白在某些细胞中出现的原因。
