Gocke E, Leer J C, Nielsen O F, Westergaard O
Nucleic Acids Res. 1978 Nov;5(11):3993-4006. doi: 10.1093/nar/5.11.3993.
Nucleoli can be isolated from Tetrahymena in a yield of 30-60%. The isolated nucleoli contain rDNA (at least 90% pure) and have a protein to DNA ratio of 30:1. The endogenous RNA-polymerase activity of the r-chromatin has the following properties: (i) The in vitro transcript has a maximal size identical to the in vivo 35S rRNA precursor, demonstrating correct termination on the gene, (ii) 79% of the in vitro transcript is complementary to cDNA of 17S and 25S rRNA which is close to the theoretical maximum for the 35S rRNA precursor, (iii) the elongation rate of the endogenous RNA-polymerase molecules is 9-12 nucleotides/sec, (iv) an average of 4-16 active RNA polymerases are associated with each rDNA molecule depending upon the preparation.
核仁可从四膜虫中分离出来，产率为30%-60%。分离出的核仁含有rDNA（纯度至少为90%），蛋白质与DNA的比例为30:1。r染色质的内源性RNA聚合酶活性具有以下特性：(i)体外转录本的最大大小与体内35S rRNA前体相同，表明在基因上正确终止；(ii)79%的体外转录本与17S和25S rRNA的cDNA互补，这接近35S rRNA前体的理论最大值；(iii)内源性RNA聚合酶分子的延伸速率为9-12个核苷酸/秒；(iv)根据制备情况，每个rDNA分子平均有4-16个活性RNA聚合酶与之相关。
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