McBride A E, Taylor S J, Shalloway D, Kirkegaard K
Department of Microbiology and Immunology, Stanford University School of Medicine, California 94305-5127, USA.
Exp Cell Res. 1998 May 25;241(1):84-95. doi: 10.1006/excr.1998.4047.
The protein Sam68 (Src-associated in mitosis, 68 kDa) has been found to bind to SH2 and to SH3 domain-containing proteins and to RNA. Although its protein-protein interactions implicate Sam68 in cell signaling, the significance of its RNA binding remains obscure. In most cells, Sam68 shows diffuse nucleoplasmic staining. Upon treatment with transcription inhibitors, however, Sam68 localize into punctate nuclear structures. Mutant forms of mouse Sam68 were overexpressed in human cells to test the importance of the KH domain, which is required for RNA binding, in the intracellular localization of Sam68. A small deletion within the KH domain (delta 206-218) or point mutation I184N had no effect upon the localization of overexpressed Sam68. Sam68 that contained a deletion of the entire KH domain (delta KH, delta 157-256) or point mutation G178E, however, localized to distinct nuclear spots. Furthermore, delta KH Sam68, unlike wild-type Sam68 and several other mutant Sam68 proteins, did not relocalize upon poliovirus infection and caused the normally cytoplasmic viral polymerase to localize to the nuclear spots. Thus both ongoing transcription and an intact KH domain are crucial determinants of the dynamic intracellular localization of Sam68.
已发现蛋白质Sam68（有丝分裂相关的Src蛋白，68 kDa）可与含SH2和SH3结构域的蛋白质以及RNA结合。尽管其蛋白质 - 蛋白质相互作用表明Sam68参与细胞信号传导，但其RNA结合的意义仍不清楚。在大多数细胞中，Sam68呈现弥漫性核质染色。然而，在用转录抑制剂处理后，Sam68定位于点状核结构。小鼠Sam68的突变形式在人细胞中过表达，以测试RNA结合所需的KH结构域在Sam68细胞内定位中的重要性。KH结构域内的一个小缺失（δ206 - 218）或点突变I184N对过表达的Sam68的定位没有影响。然而，包含整个KH结构域缺失（δKH，δ157 - 256）或点突变G178E的Sam68定位于不同的核斑点。此外，与野生型Sam68和其他几种突变型Sam68蛋白不同，δKH Sam68在脊髓灰质炎病毒感染后不会重新定位，并导致通常位于细胞质的病毒聚合酶定位于核斑点。因此，正在进行的转录和完整的KH结构域都是Sam68动态细胞内定位的关键决定因素。
