Department of Medical Microbiology and Immunology, Creighton University School of Medicine, Omaha, NE, USA.
Department of Pathology and Microbiology, University of Nebraska Medical School, Omaha, NE, USA.
Plasmid. 2021 May;115:102567. doi: 10.1016/j.plasmid.2021.102567. Epub 2021 Feb 20.
There are currently 47 characterized species in the Naegleria genus of free-living amoebae. Each amoeba has thousands of extrachromosomal elements that are closed circular structures comprised of a single ribosomal DNA (rDNA) copy and a large non-rDNA sequence. Despite the presence of putative open reading frames and introns, ribosomal RNA is the only established transcript. A single origin of DNA replication (ori) has been mapped within the non-rDNA sequence for one species (N. gruberi), a finding that strongly indicates that these episomes replicate independently of the cell's chromosomal DNA component. This article reviews that which has been published about these interesting DNA elements and by analyzing available sequence data, discusses the possibility that different phylogenetically related clusters of Naegleria species individually conserve ori structures and suggests where the rRNA promoter and termination sites may be located.
目前，自由生活的变形虫属中的纳格里亚有 47 个特征种。每个变形虫都有数千个额外的染色体元素，这些元素是封闭的环状结构，由一个核糖体 DNA(rDNA)拷贝和一个大的非 rDNA 序列组成。尽管存在假定的开放阅读框和内含子，但核糖体 RNA 是唯一确定的转录本。在一个物种（N. gruberi）的非 rDNA 序列中已经定位了一个单一的 DNA 复制起点(ori)，这一发现强烈表明这些附加体独立于细胞的染色体 DNA 成分进行复制。本文综述了关于这些有趣的 DNA 元件的已发表的研究，并通过分析可用的序列数据，讨论了不同系统发育相关的纳格里亚种簇各自保存 ori 结构的可能性，并提出了 rRNA 启动子和终止子可能的位置。
