Loftus T M, Nguyen Y H, Stanbridge E J
Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine, California 92697, USA.
Biochemistry. 1997 Jul 8;36(27):8224-30. doi: 10.1021/bi970288d.
QM is a human cDNA originally isolated as a transcript elevated in a nontumorigenic Wilms' tumor microcell hybrid, relative to the tumorigenic parental cell line. Homologs of this gene have been identified from a large number of diverse eukaryotic species which demonstrate a high degree of conservation. The functional importance implied by this strong conservation is supported by the observation that the disruption of the yeast homolog is lethal. In spite of its apparent importance, the function of the encoded protein remains elusive. Indirect immunofluorescent cell staining of cultured human, G401 cells with an antibody to the QM protein shows a punctate staining pattern in the cytoplasm with much of the signal in a perinuclear pattern. Subcellular fractionation demonstrated an association of QM protein with the rough endoplasmic reticulum. It was possible to disrupt this association by washing microsomal membranes with 1M NaCl, suggesting a peripheral association. Proteolytic latency studies showed the protein to be exposed on the cytoplasmic face of the membrane. In situ cross-linking followed by diagonal SDS gel analysis indicates that QM exists as a member of a large protein complex. In agreement with this, QM was found to copurify with the ribosome complex. Incubation with 1 M NaCl was found to disrupt this association while having no effect on the association of core ribosomal proteins.
QM是一种人类cDNA，最初是作为一种在非致瘤性威尔姆斯瘤微细胞杂交体中相对于致瘤性亲代细胞系表达上调的转录本而分离出来的。已从大量不同的真核生物物种中鉴定出该基因的同源物，这些同源物显示出高度的保守性。酵母同源物的破坏是致命的这一观察结果支持了这种强烈保守性所暗示的功能重要性。尽管其具有明显的重要性，但编码蛋白的功能仍然难以捉摸。用针对QM蛋白的抗体对培养的人G401细胞进行间接免疫荧光细胞染色，结果显示细胞质中呈点状染色模式，大部分信号呈核周模式。亚细胞分级分离表明QM蛋白与粗面内质网相关。用1M NaCl洗涤微粒体膜可以破坏这种关联，这表明是一种外周关联。蛋白酶潜伏性研究表明该蛋白暴露在膜的细胞质面上。原位交联后进行对角线SDS凝胶分析表明，QM作为一种大蛋白复合物的成员存在。与此一致的是，发现QM与核糖体复合物共纯化。发现用1M NaCl孵育会破坏这种关联，而对核心核糖体蛋白的关联没有影响。
