Casnellie J E
J Biol Chem. 1987 Jul 15;262(20):9859-64.
The LSTRA cell line contains an elevated level of a tyrosine protein kinase of apparent molecular weight of 56,000 (pp56Tcell). Analysis of the tryptic fragments of this protein labeled in vivo with 32P shows that it contains four sites of tyrosine phosphorylation and one site of serine phosphorylation. Two of the sites of in vivo tyrosine phosphorylation are also labeled in vitro when membranes are incubated with [gamma-32P]ATP. One of the sites that is labeled in vivo and in vitro (site 1) is identical in sequence with the major site of tyrosine phosphorylation in the transforming protein of the Rous sarcoma virus. Analysis of the sites of in vivo phosphorylation in pp56Tcell from LSTRA cells treated with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) reveals that this agent induces at least four new sites of serine phosphorylation. Treatment with PMA also causes a selective reduction in the level of tyrosine phosphorylation in site 1. Thus PMA causes new sites of serine phosphorylation in pp56Tcell and reduces the amount of phosphate in one of the sites of tyrosine phosphorylation.
LSTRA细胞系含有一种表观分子量为56,000的酪氨酸蛋白激酶（pp56T细胞），其水平升高。对这种在体内用32P标记的蛋白质的胰蛋白酶片段进行分析表明，它含有四个酪氨酸磷酸化位点和一个丝氨酸磷酸化位点。当膜与[γ-32P]ATP一起孵育时，体内酪氨酸磷酸化的两个位点在体外也被标记。在体内和体外都被标记的一个位点（位点1）与劳氏肉瘤病毒转化蛋白中酪氨酸磷酸化的主要位点序列相同。对用4β-佛波醇12β-肉豆蔻酸13α-乙酸酯（PMA）处理的LSTRA细胞的pp56T细胞中体内磷酸化位点的分析表明，该试剂诱导至少四个新的丝氨酸磷酸化位点。用PMA处理还会导致位点1中酪氨酸磷酸化水平的选择性降低。因此，PMA在pp56T细胞中导致新的丝氨酸磷酸化位点，并减少酪氨酸磷酸化位点之一中的磷酸量。
