Seino Ayako, Yanagida Yasuko, Aizawa Masuo, Kobatake Eiry
Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
Biochim Biophys Acta. 2005 Jan 11;1681(2-3):166-74. doi: 10.1016/j.bbaexp.2004.11.009. Epub 2004 Dec 15.
To confirm the active involvement of the internal ribosome entry site (IRES)-dependent translation in living eukaryotes, Saccharomyces cerevisiae and HAP4 IRES were used for in vitro and in vivo experiments. Since HAP4 protein might be required for activating mRNAs transcription in yeast cells when they are released from catabolite repression, the translational efficiency of HAP4 mRNA is presumed to increase under such a condition. The in vitro experiment showed clearly that the translational mechanism was shifted from the cap-dependent to the completely IRES-dependent translation when the yeast cells were derepressed from catabolite repression. From in vivo experiment, it was confirmed that the IRES-dependent translational efficiency was in a low level at the beginning of the stationary growth phase, and was enhanced at the glucose-exhausted phase. These results indicate that yeast cells on the catabolite derepressed condition could get a large amount of HAP4 protein for the completely IRES-dependent translation, while the IRES-dependent translational efficiency is increased. It has been proven that IRES functions directing the initiation of translation in living yeast cells.
为了证实内部核糖体进入位点（IRES）依赖性翻译在活的真核生物中的积极参与，酿酒酵母和HAP4 IRES被用于体外和体内实验。由于当酵母细胞从分解代谢物阻遏中释放出来时，可能需要HAP4蛋白来激活mRNA转录，因此推测在这种情况下HAP4 mRNA的翻译效率会增加。体外实验清楚地表明，当酵母细胞从分解代谢物阻遏中解除阻遏时，翻译机制从帽依赖性翻译转变为完全IRES依赖性翻译。从体内实验证实，IRES依赖性翻译效率在稳定生长期开始时处于低水平，而在葡萄糖耗尽期增强。这些结果表明，处于分解代谢物阻遏解除状态的酵母细胞可以通过完全IRES依赖性翻译获得大量HAP4蛋白，同时IRES依赖性翻译效率增加。已经证明IRES在活酵母细胞中指导翻译起始发挥作用。
