Hassauer M, Scheidtmann K H, Walter G
J Virol. 1986 Jun;58(3):805-16. doi: 10.1128/JVI.58.3.805-816.1986.
The phosphorylation sites of polyomavirus large T antigen from infected or transformed cells were investigated. Tryptic digestion of large T antigen from infected, 32Pi-labeled cells revealed seven major phosphopeptides. Five of these were phosphorylated only at serine residues, and two were phosphorylated at serine and threonine residues. The overall ratio of phosphoserine to phosphothreonine was 6:1. The transformed cell line B4 expressed two polyomavirus-specific phosphoproteins: large T antigen, which was only weakly phosphorylated, and a truncated form of large T antigen of 34,000 molecular weight which was heavily phosphorylated. Both showed phosphorylation patterns similar to that of large T antigen from infected cells. Peptide analyses of large T antigens encoded by the deletion mutants dl8 and dl23 or of specific fragments of wild-type large T antigen indicated that the phosphorylation sites are located in an amino-terminal region upstream of residue 194. The amino acid composition of the phosphopeptides as revealed by differential labeling with various amino acids indicated that several phosphopeptides contain overlapping sequences and that all phosphorylation sites are located in four tryptic peptides derived from a region between Met71 and Arg191. Two of the potential phosphorylation sites were identified as Ser81 and Thr187. The possible role of this modification of large T antigen is discussed.
对来自感染或转化细胞的多瘤病毒大T抗原的磷酸化位点进行了研究。对来自感染的、经³²P标记的细胞中的大T抗原进行胰蛋白酶消化，发现了7个主要的磷酸肽。其中5个仅在丝氨酸残基处磷酸化，2个在丝氨酸和苏氨酸残基处磷酸化。磷酸丝氨酸与磷酸苏氨酸的总体比例为6:1。转化细胞系B4表达两种多瘤病毒特异性磷蛋白：大T抗原，其磷酸化程度较弱；以及一种分子量为34000的大T抗原截短形式，其磷酸化程度较高。两者都显示出与来自感染细胞的大T抗原相似的磷酸化模式。对缺失突变体dl8和dl23编码的大T抗原或野生型大T抗原的特定片段进行肽分析表明，磷酸化位点位于第194位残基上游的氨基末端区域。通过用各种氨基酸进行差异标记所揭示的磷酸肽的氨基酸组成表明，几个磷酸肽包含重叠序列，并且所有磷酸化位点都位于来自Met71和Arg191之间区域的四个胰蛋白酶肽段中。其中两个潜在的磷酸化位点被确定为Ser81和Thr187。讨论了大T抗原这种修饰的可能作用。
