Pan W C, Blackburn E H
Cell. 1981 Feb;23(2):459-66. doi: 10.1016/0092-8674(81)90141-0.
A novel form of extrachromosomal rDNA has been identified in conjugating Tetrahymena cells. This rDNA consists of 11 kb linear double-stranded DNA molecules, each containing a single rRNA gene copy. The DNA sequence, tandemly repeated CCCCAA (Blackburn and Gall, 1978) found at the termini of extrachromosomal palindromic rDNA (the macronuclear form found in vegetatively growing cells), is also present at the corresponding terminus of the 11 kb rDNA. The other end of this molecule has an extra 0.3 kb segment of DNA covalently attached to the DNA region corresponding to the center of the palindromic rDNA. The kinetics of appearance and synthesis of the 11 kb rDNA early in macronuclear development are consistent with its being an intermediate in rDNA amplification.
在接合的四膜虫细胞中发现了一种新型的染色体外rDNA。这种rDNA由11 kb的线性双链DNA分子组成，每个分子包含一个单一的rRNA基因拷贝。在染色体外回文rDNA（营养生长细胞中发现的大核形式）末端发现的串联重复DNA序列CCCCAA（布莱克本和高尔，1978年），也存在于11 kb rDNA的相应末端。该分子的另一端有一个额外的0.3 kb DNA片段，共价连接到与回文rDNA中心对应的DNA区域。在大核发育早期，11 kb rDNA出现和合成的动力学与其作为rDNA扩增中间体的情况一致。
