An Unspliced Group I Intron in 23S rRNA Links Chlamydiales, Chloroplasts, and Mitochondria

Chlamydia was the only genus in the order Chlamydiales until the recent characterization of Simkania negevensis Z(T) and Parachlamydia acanthamoebae strains. The present study of Chlamydiales 23S ribosomal DNA (rDNA) focuses on a naturally occurring group I intron in the I-CpaI target site of 23S rDNA from S. negevensis. The intron, SnLSU · 1, belonged to the IB4 structural subgroup and was most closely related to large ribosomal subunit introns that express single-motif, LAGLIDADG endonucleases in chloroplasts of algae and in mitochondria of amoebae. RT-PCR and electrophoresis of in vivo rRNA indicated that the intron was not spliced out of the 23S rRNA. The unspliced 658-nt intron is the first group I intron to be found in bacterial rDNA or rRNA, and it may delay the S. negevensis developmental replication cycle by affecting ribosomal function.

直至近期完成对西门尼内基菌Z(T)（Simkania negevensis Z(T)）与棘阿米巴副衣原体（Parachlamydia acanthamoebae）菌株的特征化鉴定前，衣原体属（Chlamydia）始终是衣原体目（Chlamydiales）下唯一的属。本研究针对衣原体目23S核糖体DNA（rDNA）展开分析，重点聚焦于西门尼内基菌23S rDNA的I-CpaI靶位点中天然存在的第一类内含子（group I intron）SnLSU·1。该内含子隶属于IB4结构亚群（IB4 structural subgroup），与藻类叶绿体及变形虫线粒体中表达单基序LAGLIDADG内切酶（single-motif, LAGLIDADG endonucleases）的大型核糖体亚基内含子亲缘关系最为密切。针对体内核糖体RNA（in vivo rRNA）开展的逆转录聚合酶链反应（RT-PCR）与电泳实验结果显示，该内含子并未从23S rRNA中被剪接移除。这个长度为658个核苷酸（nt）的未剪接内含子，是首个在细菌rDNA或rRNA中发现的第一类内含子，其或可通过影响核糖体功能，延缓西门尼内基菌的发育复制周期。