Nguyen Y H, Mills A A, Stanbridge E J
Department of Microbiology and Molecular Genetics, College of Medicine, University of California at Irvine 92697, USA.
J Cell Biochem. 1998 Feb 1;68(2):281-5.
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. The QM gene encodes a 24 kDa basic protein that peripherally associates with the ribosomes. Recently, the gene for this protein has also been shown in Saccharomyces cerevisiae to encode an essential 60S ribosomal subunit protein that is required for the joining of the 40S and 60S subunits. Since the association of QM with ribosomes can be disrupted with 1M NaCl, which has no effect on the association of core ribosomal proteins, indirect immunofluorescent cell staining was performed to colocalize the QM protein with the human large P-antigen, a core ribosomal protein of the 60S subunit, and to determine whether the assembly of the QM protein onto the 60S ribosomal subunit occurs in the nucleolus or in the cytoplasm. Our results reveal that QM co-localizes with the large P-antigen only to the cytoplasm where the rough endoplasmic reticulum is found and not to the nucleolus where ribosome assembly occurs. This finding suggests that the QM protein is most likely involved in a late step of the 60S subunit assembly and is added to the 60S ribosomal subunit in the cytoplasm and not in the nucleolus.
QM是一种人类cDNA，最初是作为一种在非致瘤性肾母细胞瘤微细胞杂种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。QM基因编码一种24kDa的碱性蛋白，该蛋白与核糖体周边结合。最近，在酿酒酵母中也发现该蛋白的基因编码一种必需的60S核糖体亚基蛋白，它是40S和60S亚基结合所必需的。由于QM与核糖体的结合可以被1M NaCl破坏，而1M NaCl对核心核糖体蛋白的结合没有影响，因此进行了间接免疫荧光细胞染色，以使QM蛋白与人类大P抗原（60S亚基的一种核心核糖体蛋白）共定位，并确定QM蛋白在60S核糖体亚基上的组装是发生在核仁还是细胞质中。我们的结果显示，QM仅与大P抗原在发现粗面内质网的细胞质中共定位，而不与发生核糖体组装的核仁共定位。这一发现表明，QM蛋白很可能参与60S亚基组装的后期步骤，并在细胞质而非核仁中添加到60S核糖体亚基上。
