Characterization of ribosomal RNA synthesis in a gene dosage mutant: the relationship of topoisomerase I and chromatin structure to transcriptional activity.
Characterization of ribosomal RNA synthesis in a gene dosage mutant: the relationship of topoisomerase I and chromatin structure to transcriptional activity.
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DOI：
10.1083/jcb.105.4.1501
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发表时间：
1987-10
影响因子：
7.8
通讯作者：
Bloom, S E
中科院分区：
文献类型：
--
作者：
Muscarella, D E;Vogt, V M;Bloom, S E
编码18 S、5.8S和28 S核糖体RNA（rRNA）的基因在核仁组织者区（NOR）串联重复。鸡的NORs映射到一对微染色体上。先前已经描述了一个鸡系，其包含对于该染色体为二体、三体或四体的个体，并且每个细胞分别具有两个、三个或四个核仁和NOR。非整倍体动物显示每个细胞的rRNA基因拷贝数成比例增加。但是，尽管rDNA剂量增加，成熟rRNA的水平在来自非整倍体鸡的细胞中被调节至正常水平（Muscarella，D.E.，V.M.沃格特和S.E. Bloom，1985，J. Cell Biol.，101：1749-1756）。本文讨论的问题是如何调节成熟的rRNA合成发生在细胞中的rDNA水平升高。对鸡胚成纤维细胞（CEF）中rRNA转录的分析显示，所有三种基因型的rRNA合成和加工的相对速率以及每个细胞的前体rRNA的量是相似的。染色质结构的比较，确定从CEFs消化DNA酶I的细胞核中的rDNA的敏感性，揭示了一些非整倍体细胞的rRNA基因更耐消化比相应的序列中的二体细胞。还使用化合物喜树碱测定了拓扑异构酶I在rDNA上的分布，喜树碱在拓扑异构酶-DNA复合物中引入单链和双链断裂。喜树碱诱导的裂解的定量显示，在非整倍体细胞中比在二体细胞中更大比例的rRNA基因对裂解具有抗性，因此没有可检测量的拓扑异构酶I。这些结果表明，通过使用rRNA基因的一个子集来实现具有升高的rDNA水平的CEF中rRNA合成的调节。
The genes encoding 18S, 5.8S, and 28S ribosomal RNA (rRNA) are tandemly repeated at the nucleolus organizer region (NOR). The NORs in the chicken map to one pair of microchromosomes. A line of chickens that contains individuals that are either disomic, trisomic, or tetrasomic for this chromosome, and have two, three, or four nucleoli and NORs, per cell, respectively, has been described previously. Aneuploid animals display a proportional increase in the rRNA gene copy number per cell. But, despite an increase in rDNA dosage, the levels of mature rRNA are regulated to normal levels in cells from aneuploid chickens (Muscarella, D.E., V.M. Vogt, and S.E. Bloom, 1985, J. Cell Biol., 101:1749-1756). This paper addresses the question of how regulation of mature rRNA synthesis occurs in cells with elevated levels of rDNA. An analysis of rRNA transcription in chicken embryo fibroblasts (CEFs) revealed that the relative rates of rRNA synthesis and processing and the amounts of precursor rRNA per cell are similar for all three genotypes. A comparison of chromatin structure, as determined by sensitivity of rDNA in nuclei from CEFs to digestion by DNase I, revealed that some of the rRNA genes from aneuploid cells are more resistant to digestion than corresponding sequences in the disomic cells. A determination of the distribution of topoisomerase I on rDNA has also been performed using the compound camptothecin, which introduces single- and double-strand breaks in topoisomerase-DNA complexes. Quantitation of camptothecin-induced cleavages revealed that a larger proportion of the rRNA genes in aneuploid cells was resistant to cleavage than in disomic cells, and therefore have no detectable amounts of topoisomerase I. These results suggest that the regulation of rRNA synthesis in CEFs with elevated levels of rDNA is achieved by the use of a subset of the rRNA genes.