Zu K, Sikes M L, Beyer A L
Department of Microbiology, University of Virginia, Charlottesville 22908, USA.
RNA. 1998 Dec;4(12):1585-98. doi: 10.1017/s135583829898102x.
We analyzed the roles of the three domains of a Drosophila hnRNP A1 homolog by expression of wild-type and mutant versions of HRB87F/hrp36 in Drosophila melanogaster. HRB87F/hrp36 is one of two Drosophila proteins that is most similar to mammalian A1 hnRNP, and like A1, consists of two copies of the RNA-binding domain (RBD) motif followed by a glycine-rich domain (GRD). The role of the domains in nuclear localization and RNA binding to polytene chromosomal sites was determined. RBD-1 and the GRD were largely responsible for both the cellular location of the protein and for the typical chromosomal distribution pattern of the protein at sites of PolII transcription. RBD-1 also provided a role in the exon-skipping activity of the protein that was not provided by RBD-2. On the other hand, RBD-2 and the GRD were responsible for the very limited chromosomal distribution pattern seen upon heat shock, when HRB87F/hrp36 is sequestered at heat-shock puff 93D, which encodes a long nucleus-restricted RNA. Thus, these studies indicate that the two RBDs function independently of each other but in concert with the GRD. In addition, the self-association property of the GRD was strikingly evident in these overexpressed proteins.
我们通过在黑腹果蝇中表达野生型和突变型的HRB87F/hrp36，分析了果蝇hnRNP A1同源物三个结构域的作用。HRB87F/hrp36是果蝇中与哺乳动物A1 hnRNP最相似的两种蛋白质之一，与A1一样，由两个RNA结合结构域（RBD）基序拷贝组成，后面跟着一个富含甘氨酸的结构域（GRD）。确定了这些结构域在核定位以及RNA与多线染色体位点结合中的作用。RBD-1和GRD在很大程度上决定了蛋白质的细胞定位以及该蛋白质在PolII转录位点的典型染色体分布模式。RBD-1在该蛋白质的外显子跳跃活性中也发挥了作用，而RBD-2则没有此作用。另一方面，RBD-2和GRD决定了热休克时观察到的非常有限的染色体分布模式，此时HRB87F/hrp36被隔离在热休克泡93D处，该位点编码一种长的核限制RNA。因此，这些研究表明两个RBD相互独立发挥作用，但与GRD协同作用。此外，GRD的自缔合特性在这些过表达的蛋白质中非常明显。
