Schnare M N, Heinonen T Y, Young P G, Gray M W
J Biol Chem. 1986 Apr 15;261(11):5187-93.
We show here that in the mitochondria of Tetrahymena pyriformis, the small subunit (SSU) rRNA is discontinuous, being comprised of two separate components which we term "alpha" (a novel low molecular weight RNA, approximately equal to 200 nucleotides long) and "beta" (a previously described 14 S RNA). The SSU alpha rRNA has been sequenced in its entirety; it represents the immediate 5'-terminal domain of conventional SSU rRNA. The sequences at the ends of the SSU beta rRNA have also been determined; they show that this molecule corresponds to the 3'-terminal 7/8 of conventional SSU rRNA. A 2.5-kilobase pair XbaI restriction fragment of T. pyriformis mitochondrial DNA which contains the SSU alpha and SSU beta rRNA genes was cloned and its complete nucleotide sequence was determined. This revealed that the genes encoding the two segments of SSU rRNA are separated by a 54-base pair (A + T)-rich spacer. The alpha and beta sequences can be fitted to a generalized secondary structure model for eubacterial 16 S rRNA, with the two RNA species associating through long range interactions to form base-paired regions characteristic of SSU rRNA. In this model, the spacer is situated in a region of pronounced primary and secondary structural variation among SSU rRNAs. The significance of these findings with respect to rRNA biosynthesis and processing and the possible evolutionary relationship between spacers and variable regions in rRNA genes is discussed.
我们在此表明，在梨形四膜虫的线粒体中，小亚基（SSU）rRNA是不连续的，由两个独立的组分组成，我们将其分别称为“α”（一种新的低分子量RNA，长度约为200个核苷酸）和“β”（一种先前描述的14S RNA）。SSUαrRNA已被全部测序；它代表传统SSU rRNA紧邻5'-末端的结构域。SSUβrRNA末端的序列也已确定；结果表明该分子对应于传统SSU rRNA的3'-末端7/8。包含SSUα和SSUβrRNA基因的梨形四膜虫线粒体DNA的一个2.5千碱基对的XbaI限制性片段被克隆，并确定了其完整的核苷酸序列。这揭示了编码SSU rRNA两段的基因被一个富含54个碱基对（A + T）的间隔区隔开。α和β序列可以与真细菌16S rRNA的广义二级结构模型相匹配，这两种RNA通过长程相互作用结合形成SSU rRNA特有的碱基配对区域。在这个模型中，间隔区位于SSU rRNA中一级和二级结构显著变化的区域。讨论了这些发现对于rRNA生物合成和加工的意义以及间隔区与rRNA基因可变区之间可能的进化关系。
