Miller O L, Beatty B R
Science. 1969 May 23;164(3882):955-7. doi: 10.1126/science.164.3882.955.
The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules. Visualization of these genes is possible because many precursor molecules are simultaneously synthesized on each gene. Individual genes are separated by stretches of DNA that apparently are not transcribed at the time of synthesis of precursor rRNA in the extrachromosomal nucleoli.
两栖动物卵母细胞中染色体外核仁的存在，使得对编码核糖体RNA前体分子的基因进行分离和电子显微镜观察成为可能。这些基因能够被观察到，是因为每个基因上同时合成了许多前体分子。各个基因被一段段DNA隔开，在染色体外核仁中合成前体rRNA时，这些DNA显然不被转录。
