The genes encoding the ribosomal RNA (rRNA) subunits of the amoeba Naegleria gruberi are encoded in a relatively uncommon arrangement: on a circular extrachromosomal DNA element with each organism carrying about 4,000 copies of the element. As complete sequence analysis of the N. gruberi chromosomal DNA revealed no copy of the rRNA genes, these extrachromosomal elements must therefore replicate autonomously. We reported elsewhere the molecular cloning and the complete sequence analysis of the entire rRNA gene-containing element of N. gruberi (strain EG_B). Using neutral/neutral two-dimensional agarose electrophoresis, the region in the element enclosing the single replication origin using DNA from asynchronous and axenically propagated N. gruberi populations was localized within a 2.1 kbp fragment located approximately 2,300 bp from the 18S rRNA gene and 3,700 bp from the 28S rRNA gene. The results indicate that replication occurs from a single origin via a theta-type mode of replication rather than by a rolling circle mode. Further, G-quadruplex elements, often located near DNA replication origins, occur in and near this fragment in a repeated sequence.

编码变形虫Naegleria gruberi的核糖体RNA（rRNA）亚基的基因以相对不常见的排列编码：在环状染色体外DNA元件上，每个生物体携带约4,000份该元件。由于对N. gruberi染色体DNA的完整序列分析显示没有rRNA基因的拷贝，因此这些染色体外元件必须自主复制。我们在其他地方报告了N. gruberi（菌株EG _B的整个包含rRNA基因的元件的分子克隆和完整序列分析）。使用中性/中性二维琼脂糖电泳，使用来自异步和轴生繁殖的N. gruberi种群的DNA封闭单个复制起点的元件中的区域位于一个2.1 kbp的片段中，该片段位于距离18 S rRNA基因约2,300 bp和3,700 bp的位置28 S rRNA基因的bp 。结果表明复制是通过θ型复制模式而不是滚环模式从单个起点发生的。此外，通常位于DNA复制起点附近的G-四链体元件以重复序列出现在该片段中或附近。