Zahn K, Inui M, Yukawa H
Research Institute of Innovative Technology for the Earth, 9-2 Kizugawadai, Kizu-Soraku, Kyoto 619-0292, Japan.
Nucleic Acids Res. 2000 Dec 1;28(23):4623-33. doi: 10.1093/nar/28.23.4623.
Widespread occurrence of a separate small RNA derived from the 5'-end of 23S rRNA and of an intervening sequence (IVS) which separates this domain from the main segment of 23S rRNA in the alpha-proteobacteria implies that processing reactions which act to excise the IVS are also maintained in this group. We previously characterized the first example of processing of this IVS in Rhodopseudomonas palustris, which is classified with the Bradyrhizobia In this case, IVS excision occurs by a multistep process and RNase III appears to act at an early step. Here, we characterize in vivo and in vitro IVS processing in two other related, but phenotypically distinct, Bradyrhizobia We also examine in vivo and in vitro processing of rRNA precursors from a more distantly related alpha-proteobacterium, Rhodobacter sphaeroides which produces a separate 5' 23S rRNA domain but has different sequences in the 5' 23S rRNA IVS. The details of the in vivo processing of all of the Bradyrhizobial rRNAs closely resemble the R. palustris example and in vitro studies suggest that all of the Bradyrhizobia utilize RNase III in the first step of IVS cleavage. Remarkably, in vivo and in vitro studies with R.sphaeroides indicate that initial IVS cleavage uses a different mechanism. While the mechanism of IVS cleavage differs among these alpha-proteobacteria, in all of these cases the limits of the internal segments processed in vivo are almost identical and occur far beyond the initial cleavage sites within the IVSs. We propose that these bacteria possess common secondary maturation pathways which enable them to generate similarly processed 23S rRNA 5'- and 3'-ends.
在α-变形菌中，广泛存在一种源自23S rRNA 5'端的独立小RNA以及一个将该结构域与23S rRNA主片段分隔开的间隔序列（IVS），这意味着切除IVS的加工反应在该类群中也得以保留。我们之前对沼泽红假单胞菌中该IVS加工的首个实例进行了表征，沼泽红假单胞菌与慢生根瘤菌同属一类。在这种情况下，IVS切除通过多步过程发生，并且RNase III似乎在早期步骤发挥作用。在此，我们对另外两种相关但表型不同的慢生根瘤菌的体内和体外IVS加工进行了表征。我们还研究了来自亲缘关系更远的α-变形菌球形红杆菌的rRNA前体的体内和体外加工，球形红杆菌产生一个独立的5' 23S rRNA结构域，但在5' 23S rRNA IVS中有不同序列。所有慢生根瘤菌rRNA的体内加工细节与沼泽红假单胞菌的实例非常相似，体外研究表明所有慢生根瘤菌在IVS切割的第一步都利用RNase III。值得注意的是，对球形红杆菌的体内和体外研究表明，初始IVS切割使用不同的机制。虽然这些α-变形菌中IVS切割的机制不同，但在所有这些情况下，体内加工的内部片段的界限几乎相同，并且发生在IVS内的初始切割位点之外很远的地方。我们提出这些细菌拥有共同的二级成熟途径，使它们能够产生加工方式相似的23S rRNA 5'端和3'端。
