Garrett T A, Pabón-Peña L M, Gokaldas N, Epstein L M
Department of Chemistry, Florida State University, Tallahassee 32306-3050, USA.
RNA. 1996 Jul;2(7):699-706.
A number of RNAs that infect plants self-cleave using a domain called the hammerhead. The consensus plant hammerhead has three base paired stem structures. Stems I and III flank the cleaved phosphodiester and are connected to stem II by two unpaired and highly conserved sequences. We demonstrated previously that satellite 2 transcripts from the newt, Notophthalmus viridescens, use a modified hammerhead structure for self-cleavage. Here we show that hammerheads with similar modifications occur in satellite 2 from species representing two additional families of salamanders (Ambystoma talpoideum and Amphiuma tridactylum). The distinctive features of the modified satellite 2 hammerheads include unusually short stem III regions and internally looped extensions to stem I that are required for cleavage. However, despite the strict nucleotide requirement in the internal stem I loop of the newt hammerhead, the details of the stem I extensions differ in the three salamanders. An analysis of chimeric transcripts indicated that, in order for a specific stem I extension to be functional, it must be compatible with other regions of the modified satellite 2 hammerhead. One such region is stem II, and a mutational analysis has confirmed that there are specific sequence and/or structural requirements in stem II.
一些感染植物的RNA利用一种称为锤头状结构域的区域进行自我切割。植物锤头状结构域的共有序列具有三个碱基配对的茎结构。茎I和茎III位于切割的磷酸二酯键两侧，并通过两个未配对且高度保守的序列与茎II相连。我们之前证明，来自蝾螈（绿红东美螈）的卫星2转录本使用一种经过修饰的锤头状结构进行自我切割。在此我们表明，在另外两个蝾螈科（美洲钝口螈和三趾两栖鲵）物种的卫星2中也存在具有类似修饰的锤头状结构。修饰后的卫星2锤头状结构的独特特征包括异常短的茎III区域以及茎I内部环状延伸，这些是切割所必需的。然而，尽管蝾螈锤头状结构的茎I内部环对核苷酸有严格要求，但在这三种蝾螈中，茎I延伸的细节有所不同。对嵌合转录本的分析表明，为了使特定的茎I延伸具有功能，它必须与修饰后的卫星2锤头状结构的其他区域兼容。其中一个这样的区域是茎II，突变分析已证实茎II存在特定的序列和/或结构要求。
