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标题：Visualization of a group II intron in the 23S rRNA of a stable ribosome
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作者：Jacoba G. Slagter-Jäger ; Gregory S. Allen ; Dorie Smith 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2006
卷号：103
期号：26
页码：9838-9843
DOI：10.1073/pnas.0603956103
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Thousands of introns have been localized to rRNA genes throughout the three domains of life. The consequences of the presence of either a spliced or an unspliced intron in a rRNA for ribosome assembly and packaging are largely unknown. To help address these questions, and to begin an intron imaging study, we selected a member of the self-splicing group II intron family, which is hypothesized to be the progenitor not only of spliceosomal introns but also of non-LTR retrotransposons. We cloned the self-splicing group II Ll.LtrB intron from Lactococcus lactis into L. lactis 23S rRNA. The 2,492-nt Ll.LtrB intron comprises a catalytic core and an ORF, which encodes a protein, LtrA. LtrA forms a ribonucleoprotein (RNP) complex with the intron RNA to mediate splicing and mobility. The chimeric 23S-intron RNA was shown to be splicing proficient in its native host in the presence of LtrA. Furthermore, a low-resolution cryo-EM reconstruction of the L. lactis ribosome fused to the intron-LtrA RNP of a splicing-defective Ll.LtrB intron was obtained. The image revealed the intron as a large, well defined structure. The activity and structural integrity of the intron indicate not only that it can coexist with the ribosome but also that its presence permits the assembly of a stable ribosome. Additionally, we view our results as a proof of principle that ribosome chimeras may be generally useful for studying a wide variety of structured RNAs and RNP complexes that are not amenable to NMR, crystallographic, or single-particle cryo-EM methodologies.
关键词：cryo-EM ; ribonucleoprotein complex ; ribosome–intron chimera