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Bing Xia Haiping Ke Wei Jiang Masayori Inouye 《The Journal of biological chemistry》2002,277(8):6005-6011
The 5'-end region of cspA mRNA contains a Cold Box sequence conserved among several cold-shock mRNAs. This region forms a stable stem-loop structure followed by an AU-rich sequence. Here we show that the Cold Box region is essential for the normal scale of cspA mRNA induction after cold shock because a deletion of the stem-loop significantly destabilizes the mRNA and reduces the cold shock-induced cspA mRNA amount by approximately 50%. The AU-rich track, however, slightly destabilizes the mRNA. The integrity of the stem is essential for the stabilizing function, whereas that of the loop sequence is less important. Overexpression of a mutant cspA mRNA devoid of both the AUG initiation codon and the coding sequence results in a severe growth inhibition at low temperature along with a derepression of the chromosomal cspA expression. Furthermore, the overexpressed RNA is stably associated with the 30 S and 70 S ribosomes. Our results demonstrate that the AUG initiation codon and the coding region containing the downstream box are not required for cspA mRNA to bind ribosomes and that the 5'-untranslated region by itself has a remarkable affinity to ribosomes at low temperature. 相似文献
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Summary To assay the functional significance of the multiple but closely related - and -tubulin polypeptides (termed isotypes) that are expressed in mammalian cells, we have generated a number of sera that uniquely discriminate among these isotypes. These sera have been used to demonstrate that there is no subcellular sorting of either - or -tubulin isotypes among microtubules of diverse function, either in cells growing in culture or in tissues consisting of cell types that contain specialized kinds of microtubule. In spite of this failure to segregate between functionally distinct kinds of microtubule, the fact that isotype-specific amino acid sequences have been strictly conserved over extensive periods of evolutionary time argues persuasively for a functional role for the different tubulin gene products. One possibility is that they are required for specific interactions with microtubule associated proteins (MAPs), and that tubulin isotypes have coevolved with different cell type-specific MAPs with which they must interact. We have tested this hypothesis by examining the distribution of -tubulin isotypes in mammalian cerebellum in relationship to the known patterns of expression of a number of MAPs, and find that these patterns correlate in the case of M 2 and MAP 3, and M 6 and MAP 1 a. These data, plus emerging data based on a structural analysis of tau, MAP 1 b and MAP 2 obtained via sequence determination of cloned cDNAs, are discussed in terms of the possible functional significance of tubulin isotype/MAP interactionsin vivo. 相似文献
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作者合成了阴离子型和阳离子型葡聚糖,以此为载体,用CNBr活化其剩余羟基,固定化了葡萄糖淀粉酶和葡萄糖异构酶。就离子型载体对固定化酶的蛋白载量、最适pH和热稳定性等的影响做了考察。发现固定化酶的蛋白载量不仅与载体的电性质有关,也与酶分子自身的电性质有关。当载体电性质与酶蛋白电性质相反时,固定化酶的蛋白载量增加,热稳定性提高、载体电性质与酶蛋白电性质相同时,固定化酶的蛋白载量不变或下降,其热稳定性不变。作者还发现当离子型载体孔度和体系缓冲液浓度一定时,酶分子能否进入多孔性载体内部,对其最适pH是否变化影响极大。若酶分子仅被连接在载体的外表层,其最适pH不发生变化,反之亦然。作者还观察到当多糖类载体引入氨基或羧基后,大大增强了其抵抗微生物侵蚀的能力。 相似文献
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T6 DNA topoisomerase has been purified from bacteriophage T6 infected Escherichia coli. Unlike the T4 DNA topoisomerase which has three subunits, it consists of two subunits of molecular weights 75,000 and 51,000. They are the products of T6 genes 39 and 52, respectively. The purified T6 enzyme can stimulate in vitro T6 DNA replication. It has an ATP-dependent DNA relaxation activity similar to the T4 enzyme. Either ATP or dATP can be used in both reactions. Using a "Western blotting" and radioimmuno-detection methods, we show that T6 39 subunit contains protein sequences specified by both the T4 39 and 60 genes. The 52-proteins of both phages appear to be identical. The T4 and T6 topoisomerase genes represent a naturally occurring example of gene separation or fusion. 相似文献
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利用人粒细胞集落刺激因子(hG-CSF)cDNA3′端非翻译区(3′-UTR)中存在的DraⅠ酶切位点,通过部分酶切与完全酶切,删除3′-UTR不同长度,构建了四种hG-CSFcDNA瞬时重组表达质粒。转染COS-7细胞后,生物活性测定结果提示,hG-CSFcDNA3′-UTR对其表达起负调控作用,其关键性序列位于紧接终止密码子TGA下游的65bp范围内,3′-UTR对hG-CSFcDNA表达的影响与转录水平的差别有一定关系。 相似文献