Spann P, Feinerman M, Sperling J, Sperling R
Department of Genetics, Hebrew University of Jerusalem, Israel.
Proc Natl Acad Sci U S A. 1989 Jan;86(2):466-70. doi: 10.1073/pnas.86.2.466.
We have previously shown that nuclear transcripts of the multifunctional enzyme, carbamoyl-phosphate synthetase, aspartate transcarbamylase, dihydroorotase RNA can be released from nuclei of Syrian hamster cells as compact ribonucleoprotein (RNP) particles that sediment at the 200S region in a sucrose gradient. The 200S nuclear RNP particles contain U1, U2, and U6 small nuclear RNPs, which are known to be required for splicing of pre-mRNA, as integral components of the particles. In this study we demonstrate that nuclear transcripts of dihydrofolate reductase in Syrian hamster cells and of beta-actin in both Syrian hamster and human cells are also released from the respective nuclei as 200S particles--despite the difference in length of these RNAs. Electron microscopy of the 200S particles revealed discrete compact composite structures with a cross section of approximately 50 nm. Finding that two more nuclear RNAs from two different cell types and two different species are released as 200S RNP particles suggests a general mode for packaging of heterogeneous nuclear RNA in large compact RNP particles the size of which is independent of the RNA length.
我们之前已经表明，多功能酶氨甲酰磷酸合成酶、天冬氨酸转氨甲酰酶、二氢乳清酸酶RNA的核转录本可以从叙利亚仓鼠细胞的细胞核中释放出来，成为在蔗糖梯度中于200S区域沉降的致密核糖核蛋白（RNP）颗粒。200S核RNP颗粒包含U1、U2和U6小核RNP，它们作为颗粒的组成成分，已知是前体mRNA剪接所必需的。在本研究中，我们证明叙利亚仓鼠细胞中二氢叶酸还原酶的核转录本以及叙利亚仓鼠和人类细胞中β-肌动蛋白的核转录本也以200S颗粒的形式从各自的细胞核中释放出来——尽管这些RNA的长度有所不同。对200S颗粒的电子显微镜观察显示出离散的致密复合结构，其横截面约为50纳米。发现来自两种不同细胞类型和两个不同物种的另外两种核RNA以200S RNP颗粒的形式释放，这表明在大小与RNA长度无关的大型致密RNP颗粒中包装异质核RNA的一种普遍模式。
