Si K, Maitra U
Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA.
Mol Cell Biol. 1999 Feb;19(2):1416-26. doi: 10.1128/MCB.19.2.1416.
Eukaryotic translation initiation factor 6 (eIF6) binds to the 60S ribosomal subunit and prevents its association with the 40S ribosomal subunit. The Saccharomyces cerevisiae gene that encodes the 245-amino-acid eIF6 (calculated Mr 25,550), designated TIF6, has been cloned and expressed in Escherichia coli. The purified recombinant protein prevents association between 40S and 60S ribosomal subunits to form 80S ribosomes. TIF6 is a single-copy gene that maps on chromosome XVI and is essential for cell growth. eIF6 expressed in yeast cells associates with free 60S ribosomal subunits but not with 80S monosomes or polysomal ribosomes, indicating that it is not a ribosomal protein. Depletion of eIF6 from yeast cells resulted in a decrease in the rate of protein synthesis, accumulation of half-mer polyribosomes, reduced levels of 60S ribosomal subunits resulting in the stoichiometric imbalance in the 40S/60S subunit ratio, and ultimately cessation of cell growth. Furthermore, lysates of yeast cells depleted of eIF6 remained active in translation of mRNAs in vitro. These results indicate that eIF6 does not act as a true translation initiation factor. Rather, the protein may be involved in the biogenesis and/or stability of 60S ribosomal subunits.
真核生物翻译起始因子6（eIF6）与60S核糖体亚基结合，并阻止其与40S核糖体亚基结合。编码245个氨基酸的eIF6（计算分子量为25,550）的酿酒酵母基因，命名为TIF6，已被克隆并在大肠杆菌中表达。纯化的重组蛋白可阻止40S和60S核糖体亚基之间结合形成80S核糖体。TIF6是一个单拷贝基因，定位于第十六号染色体，对细胞生长至关重要。在酵母细胞中表达的eIF6与游离的60S核糖体亚基结合，但不与80S单体或多聚核糖体结合，这表明它不是一种核糖体蛋白。酵母细胞中eIF6的缺失导致蛋白质合成速率下降、半聚体多核糖体积累、60S核糖体亚基水平降低，导致40S/60S亚基比例的化学计量失衡，最终细胞生长停止。此外，缺乏eIF6的酵母细胞裂解物在体外mRNA翻译中仍保持活性。这些结果表明，eIF6并非真正的翻译起始因子。相反，该蛋白可能参与60S核糖体亚基的生物合成和/或稳定性。
