Di Fruscio M, Chen T, Bonyadi S, Lasko P, Richard S
Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research, Montreal, Quebec H3T 1E2.
J Biol Chem. 1998 Nov 13;273(46):30122-30. doi: 10.1074/jbc.273.46.30122.
Sam68 is a member of a growing family of RNA-binding proteins that contains an extended K homology (KH) domain embedded in a larger domain called the GSG (GRP33, Sam68, GLD1) domain. To identify GSG domain family members, we searched data bases for expressed sequence tags encoding related portions of the Sam68 KH domain. Here we report the identification of two novel Drosophila KH domain proteins, which we termed KEP1 (KH encompassing protein) and SAM. SAM bears sequence identity with mammalian Sam68 and may be the Drosophila Sam68 homolog. We demonstrate that SAM, KEP1, and the recently identified Drosophila Who/How are RNA-binding proteins that are able to self-associate into homomultimers. The GSG domain of KEP1 and SAM was necessary to mediate the RNA binding and self-association. To elucidate the cellular roles of these proteins, SAM, KEP1, and Who/How were expressed in mammalian and Drosophila S2 cells. KEP1 and Who/How were nuclear and SAM was cytoplasmic. The expression of KEP1 and SAM, but not Who/How, activated apoptotic pathways in Drosophila S2 cells. The identification of KEP1 and SAM implies that a large GSG domain protein family exists and helps redefine the boundaries of the GSG domain. Taken together, our data suggest that KEP1 and SAM may play a role in the activation or regulation of apoptosis and further implicate the GSG domain in RNA binding and oligomerization.
Sam68是一个不断壮大的RNA结合蛋白家族的成员，该家族包含一个延伸的K同源性（KH）结构域，此结构域嵌入一个更大的称为GSG（GRP33、Sam68、GLD1）的结构域中。为了鉴定GSG结构域家族成员，我们在数据库中搜索编码Sam68 KH结构域相关部分的表达序列标签。在此，我们报告鉴定出两种新的果蝇KH结构域蛋白，我们将其命名为KEP1（包含KH结构域的蛋白）和SAM。SAM与哺乳动物的Sam68具有序列同一性，可能是果蝇Sam68的同源物。我们证明SAM、KEP1以及最近鉴定出的果蝇Who/How是能够自缔合成同多聚体的RNA结合蛋白。KEP1和SAM的GSG结构域对于介导RNA结合和自缔合是必需的。为了阐明这些蛋白在细胞中的作用，SAM、KEP1和Who/How在哺乳动物和果蝇S2细胞中表达。KEP1和Who/How定位于细胞核，而SAM定位于细胞质。KEP1和SAM的表达，而非Who/How的表达，激活了果蝇S2细胞中的凋亡途径。KEP1和SAM的鉴定意味着存在一个大型的GSG结构域蛋白家族，并有助于重新定义GSG结构域的边界。综上所述，我们的数据表明KEP1和SAM可能在凋亡的激活或调节中发挥作用，并进一步表明GSG结构域与RNA结合和寡聚化有关。
