Narita J O, Rushlow K E, Hallick R B
J Biol Chem. 1985 Sep 15;260(20):11194-9.
Euglena gracilis chloroplasts contain a 145,000-base pair chromosome that encodes genes for ribosomal, transfer, and messenger RNAs. These genes are transcribed within the organelle by chloroplast RNA polymerase activities that are specific for different classes of RNA. Two transcriptional activities have been isolated from Euglena chloroplasts. (Greenberg, B. M., Narita, J. O., DeLuca-Flaherty, C., Gruissem, W., Rushlow, K. A., and Hallick, R. B. (1984) J. Biol. Chem. 259, 14880-14887). One, the "soluble extract," contains enzymes active in tRNA transcription and processing. The other activity, the transcriptionally active chromosome, consisting of a chloroplast DNA-dependent RNA polymerase tightly bound to chloroplast DNA, only transcribes rRNA genes even though the entire chloroplast genome is present. We have extensively purified the transcriptionally active chromosome using high salt concentrations to dissociate loosely bound proteins. The result is a highly enriched extract containing three major polypeptides of Mr 116,000-118,000, 83,000-88,000, and 24,000-26,000 that retains complete selectivity for rDNA transcription. It is probable that one, or both, of the high molecular weight proteins are functional components of the DNA-dependent RNA polymerase. The identification and characterization of the transcriptionally active chromosome is a first step towards understanding how chloroplast rRNA synthesis is regulated.
纤细裸藻的叶绿体含有一条145,000个碱基对的染色体，该染色体编码核糖体RNA、转运RNA和信使RNA的基因。这些基因在细胞器内由叶绿体RNA聚合酶活性转录，这些活性对不同类别的RNA具有特异性。已经从纤细裸藻叶绿体中分离出两种转录活性。（格林伯格，B.M.，成田，J.O.，德卢卡 - 弗莱厄蒂，C.，格鲁伊斯姆，W.，拉什洛，K.A.，和哈利克，R.B.（1984年）《生物化学杂志》259，14880 - 14887）。一种是“可溶性提取物”，含有在tRNA转录和加工中具有活性的酶。另一种活性是转录活性染色体，由紧密结合在叶绿体DNA上的叶绿体DNA依赖性RNA聚合酶组成，即使整个叶绿体基因组都存在，它也只转录rRNA基因。我们使用高盐浓度广泛纯化了转录活性染色体，以解离松散结合的蛋白质。结果是一种高度富集的提取物，含有分子量为116,000 - 118,000、83,000 - 88,000和24,000 - 26,000的三种主要多肽，该提取物对rDNA转录保留了完全的选择性。很可能一种或两种高分子量蛋白质是DNA依赖性RNA聚合酶的功能成分。转录活性染色体的鉴定和表征是理解叶绿体rRNA合成如何被调控的第一步。
