To identify genes involved in signal transduction pathways that regulate T cell activation and development, murine fetal thymocytes were screened for expression of protein tyrosine kinase family members by the polymerase chain reaction. Using this approach, a non-receptor protein tyrosine kinase, txk, was identified and cloned. Tsk is expressed in thymocytes as early as fetal day 13.5 and its expression at the mRNA level continues throughout development. Txk transcripts are present in thymocytes, peripheral T cells and mast cell lines, but are not detectable in B cell macrophage/monocyte cell lines or in non-hematopoietic fetal or adult tissues. In both thymocytes and T cells, txk transcripts are down-regulated after activation with PMA and ionomycin, concanavalin A or T cell receptor cross-linking. Sequence analysis indicates that txk contains SH2, SH3 and kinase catalytic domains and belongs to the tec family of cytoplasmic protein tyrosine kinases which includes tec, itk and btk. Its unique N-terminus contains a proline-rich region, but unlike the other tec family members, does not contain a pleckstrin homology domain. The restricted expression pattern of txk and its regulation by T cell activation make it an excellent candidate for involvement in signal transduction during thymocyte development.

中文翻译：

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鼠txk：受T细胞活化调节的蛋白质酪氨酸激酶基因。

为了鉴定参与调节T细胞活化和发育的信号转导途径的基因，通过聚合酶链反应筛选了鼠胎儿胸腺细胞中蛋白酪氨酸激酶家族成员的表达。使用这种方法，鉴定并克隆了非受体蛋白酪氨酸激酶txk。Tsk最早在胎儿第13.5天在胸腺细胞中表达，并且在整个发育过程中都在mRNA水平上表达。Txk转录本存在于胸腺细胞，外周T细胞和肥大细胞系中，但在B细胞巨噬细胞/单核细胞系或非造血性胎儿或成年组织中无法检测到。在胸腺细胞和T细胞中，用PMA和离子霉素，伴刀豆球蛋白A或T细胞受体交联激活后，txk转录本被下调。序列分析表明txk包含SH2，SH3和激酶催化结构域，属于胞质蛋白酪氨酸激酶的tec家族，包括tec，itk和btk。其独特的N端包含一个富含脯氨酸的区域，但与其他tec家族成员不同，它不包含pleckstrin同源结构域。txk的限制性表达模式及其受T细胞活化的调节使其成为胸腺细胞发育过程中参与信号转导的极佳候选者。