Waggener John M, DiMario Patrick J
Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803-1715, USA.
Mol Biol Cell. 2002 Jan;13(1):362-81. doi: 10.1091/mbc.01-04-0162.
The Nopp140 gene of Drosophila maps within 79A5 of chromosome 3. Alternative splicing yields two variants. DmNopp140 (654 residues) is the sequence homolog of vertebrate Nopp140. Its carboxy terminus is 64% identical to that of the prototypical rat Nopp140. DmNopp140-RGG (688 residues) is identical to DmNopp140 throughout its first 551 residues, but its carboxy terminus contains a glycine/arginine-rich domain that is often found in RNA-binding proteins such as vertebrate nucleolin. Both Drosophila variants localize to nucleoli in Drosophila Schneider II cells and Xenopus oocytes, specifically within the dense fibrillar components. In HeLa cells, DmNopp140-RGG localizes to intact nucleoli, whereas DmNopp140 partitions HeLa nucleoli into phase-light and phase-dark regions. The phase-light regions contain DmNopp140 and endogenous fibrillarin, whereas the phase-dark regions contain endogenous nucleolin. When coexpressed, both Drosophila variants colocalize to HeLa cell nucleoli. Both variants fail to localize to endogenous Cajal bodies in Xenopus oocyte nuclei and in HeLa cell nuclei. Endogenous HeLa coilin, however, accumulates around the periphery of phase-light regions in cells expressing DmNopp140. The carboxy truncation (DmNopp140DeltaRGG) also fails to localize to Cajal bodies, but it forms similar phase-light regions that peripherally accumulate endogenous coilin. Conversely, we see no unusual accumulation of coilin in cells expressing DmNopp140-RGG.
果蝇的Nopp140基因定位于3号染色体的79A5区域内。可变剪接产生两种变体。DmNopp140（654个残基）是脊椎动物Nopp140的序列同源物。其羧基末端与典型的大鼠Nopp140的羧基末端有64%的同一性。DmNopp140-RGG（688个残基）在其前551个残基上与DmNopp140相同，但其羧基末端包含一个富含甘氨酸/精氨酸的结构域，该结构域常见于RNA结合蛋白中，如脊椎动物的核仁素。两种果蝇变体都定位于果蝇施奈德II细胞和非洲爪蟾卵母细胞的核仁中，具体位于致密纤维成分内。在HeLa细胞中，DmNopp140-RGG定位于完整的核仁，而DmNopp140将HeLa核仁分为亮区和暗区。亮区含有DmNopp140和内源性纤维蛋白，而暗区含有内源性核仁素。当共表达时，两种果蝇变体都共定位于HeLa细胞核仁。两种变体都不能定位于非洲爪蟾卵母细胞核和HeLa细胞核中的内源性卡哈尔体。然而，内源性HeLa卷曲螺旋蛋白在表达DmNopp140的细胞中亮区周围积累。羧基截短体（DmNopp140DeltaRGG）也不能定位于卡哈尔体，但它形成了类似的亮区，在其周围积累内源性卷曲螺旋蛋白。相反，在表达DmNopp140-RGG的细胞中，我们没有看到卷曲螺旋蛋白的异常积累。
