College of Fisheries and Life Science, Dalian Ocean University, Dalian 116023, China; Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Int J Biol Macromol. 2020 Mar 15;147:576-581. doi: 10.1016/j.ijbiomac.2020.01.063. Epub 2020 Jan 10.
Tetrahymena ribosomal DNA (rDNA) is an ideal system for studying eukaryotic DNA replication and gene transcription. In this study, we developed a new method to isolate rDNA from Tetrahymena cells and used it to sequence and annotate the complete 19,670 bp macronuclear rDNA minichromosome of Tetrahymena pyriformis, a species that lacks the germ-line micronucleus and is unable to undergo sexual reproduction. The key features of T. pyriformis and Tetrahymena thermophila rDNA sequences were then compared. Our results showed (i) the short inverted repeats (M repeats) essential for formation of rDNA minichromosome palindromic structure during sexual reproduction in Tetrahymena are highly conserved in T. pyriformis; (ii) in contrast to T. thermophila, which has two tandem domains that coordinately regulate rDNA replication, T. pyriformis has only a single domain; (iii) the 35S pre-rRNA precursor has 80.25% similarity between the two species; and (iv) the G + C content is higher in the transcribed region than the non-transcribed region in both species, but the GC-skew is more stable in T. pyriformis. The new isolation method and annotated information for the T. pyriformis rDNA minichromosome will provide a useful resource for studying DNA replication and chromosome copy number control in Tetrahymena.
四膜虫核糖体 DNA(rDNA)是研究真核生物 DNA 复制和基因转录的理想系统。在本研究中，我们开发了一种从四膜虫细胞中分离 rDNA 的新方法，并利用该方法对缺乏生殖系小核且无法进行有性生殖的梨形四膜虫的完整 19670bp 大核 rDNA 微染色体进行了测序和注释。然后比较了梨形四膜虫和嗜热四膜虫 rDNA 序列的主要特征。我们的结果表明：(i) 在四膜虫有性生殖过程中形成 rDNA 微染色体回文结构所必需的短反向重复序列（M 重复序列）在梨形四膜虫中高度保守；(ii) 与具有两个串联结构域以协调调控 rDNA 复制的嗜热四膜虫不同，梨形四膜虫只有一个结构域；(iii) 35S 前 rRNA 前体在两个物种之间具有 80.25%的相似性；(iv) 在两个物种中，转录区的 G+C 含量均高于非转录区，但 GC 倾斜度在梨形四膜虫中更稳定。梨形四膜虫 rDNA 微染色体的新分离方法和注释信息将为研究四膜虫 DNA 复制和染色体拷贝数控制提供有用的资源。
