Kondo K, Kowalski L R, Inouye M
Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Rutgers, Piscataway 08854-5635.
J Biol Chem. 1992 Aug 15;267(23):16259-65.
Yeast NSR1 protein is structurally related to mammalian nucleolin and is involved in ribosome synthesis as described in the preceding paper (Kondo, K., and Inouye, M. (1992) J. Biol. Chem. 267, 16252-16258). We report here the regulation of NSR1 gene expression and the effect of nsr1 deletion on growth and pre-rRNA processing after cold shock. A basal level of the transcript was detected at 30 degrees C only in exponentially growing cells and increased approximately 3-fold after cold shock to 10 degrees C. NSR1 protein level also increased about 3-fold after the shock. The nsr1 deletion caused a severe growth defect at low temperatures as well as a long growth lag after temperature shift from 30 to 10 degrees C. Northern hybridization analysis demonstrated that cold shock led to a rapid decrease in the amounts of 27 S, 20 S, and 7 S rRNA precursors in the nsr1 strain, although at 30 degrees C a major defect was observed only in 20 S pre-rRNA synthesis. Pulse-chase labeling of rRNA showed that pre-rRNA processing in the nsr1 strain was greatly impaired after cold shock. These results demonstrate that the NSR1 protein is required for normal pre-rRNA processing and cell growth in yeast when cells are exposed to abrupt temperature drop.
酵母NSR1蛋白在结构上与哺乳动物核仁素相关，并且如前文所述（近藤，K.，和井上，M.（1992年）《生物化学杂志》267卷，第16252 - 16258页）参与核糖体合成。我们在此报告NSR1基因表达的调控以及nsr1基因缺失对冷休克后生长和前体核糖体RNA（pre-rRNA）加工的影响。仅在指数生长期的细胞中于30℃检测到基础水平的转录本，冷休克至10℃后增加约3倍。冷休克后NSR1蛋白水平也增加约3倍。nsr1基因缺失在低温下导致严重的生长缺陷，以及从30℃转移至10℃后出现长时间的生长延迟。Northern杂交分析表明，冷休克导致nsr1菌株中27 S、20 S和7 S rRNA前体的量迅速减少，尽管在30℃时仅在20 S前体rRNA合成中观察到主要缺陷。rRNA的脉冲追踪标记显示，冷休克后nsr1菌株中的前体rRNA加工受到极大损害。这些结果表明，当细胞暴露于温度骤降时，NSR1蛋白是酵母中正常前体rRNA加工和细胞生长所必需的。
