NAP57, a mammalian nucleolar protein with a putative homolog in yeast and bacteria.
NAP57, a mammalian nucleolar protein with a putative homolog in yeast and bacteria.
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DOI：
10.1083/jcb.127.6.1505
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发表时间：
1994-12
期刊：
影响因子：
--
通讯作者：
Blobel G
中科院分区：
文献类型：
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作者：
Meier UT;Blobel G
我们报道了一种新的大鼠肝脏核仁蛋白的鉴定和分子特征。如所示的免疫共沉淀，这种蛋白质与以前确定的核仁蛋白，Nopp 140，在一个明显的化学计量复合物，因此被称为NAP 57（Nopp 140相关蛋白的57 kD）。免疫荧光和免疫金电子显微镜与NAP 57特异性抗体显示共定位与Nopp 140的致密纤维组成部分的核仁，卷曲体，和核质。在核质中的免疫金染色偶尔被视为在核仁和核膜之间的曲线轨道的形式，类似于先前报道的Nopp 140。这些数据表明，Nopp 140和NAP 57确实在这些核结构中彼此相关。NAP 57的cDNA推导的一级结构显示出计算分子量为52，070的蛋白质，其在其氨基和羧基末端附近含有推定的核定位信号，并且疏水氨基酸重复基序延伸跨越84个残基。与Nopp 140一样，NAP 57缺乏任何已知的RNA结合共有序列，这些序列是许多核仁蛋白的特征。数据库检索显示NAP 57是一个高度保守的蛋白质。一种假定的酵母（S. cerevisiae）同源物有71%相同。最引人注目的是，似乎还有一个较小的原核生物（E。coli和B.枯草芽孢杆菌）同源物，其与NAP 57几乎50%相同。这表明NAP 57及其推定的同源物可能在原核生物和真核生物中都具有高度保守的功能，例如核糖体蛋白和/或前核糖体组装的伴侣。
We report the identification and molecular characterization of a novel nucleolar protein of rat liver. As shown by coimmunoprecipitation this protein is associated with a previously identified nucleolar protein, Nopp140, in an apparently stoichiometric complex and has therefore been termed NAP57 (Nopp140-associated protein of 57 kD). Immunofluorescence and immunogold electron microscopy with NAP57 specific antibodies show colocalization with Nopp140 to the dense fibrillar component of the nucleolus, to coiled bodies, and to the nucleoplasm. Immunogold staining in the nucleoplasm is occasionally seen in the form of curvilinear tracks between the nucleolus and the nuclear envelope, similar to those previously reported for Nopp140. These data suggest that Nopp140 and NAP57 are indeed associated with each other in these nuclear structures. The cDNA deduced primary structure of NAP57 shows a protein of a calculated molecular mass of 52,070 that contains a putative nuclear localization signal near its amino and carboxy terminus and a hydrophobic amino acid repeat motif extending across 84 residues. Like Nopp140, NAP57 lacks any of the known consensus sequences for RNA binding which are characteristic for many nucleolar proteins. Data bank searches revealed that NAP57 is a highly conserved protein. A putative yeast (S. cerevisiae) homolog is 71% identical. Most strikingly, there also appears to be a smaller prokaryotic (E. coli and B. subtilis) homolog that is nearly 50% identical to NAP57. This indicates that NAP57 and its putative homologs might serve a highly conserved function in both pro- and eukaryotes such as chaperoning of ribosomal proteins and/or of preribosome assembly.