Open AccessVisualization of a group II intron in the 23S rRNA of a stable ribosome
Author(s) -
Jacoba G. SlagterJäger,
Gregory S. Allen,
Dorie Smith,
Ingrid Hahn,
Joachim Frank,
Marlene Belfort
Publication year - 2006
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0603956103
Subject(s) - ribosome , 23s ribosomal rna , intron , ribosomal rna , biology , genetics , computational biology , group (periodic table) , group i catalytic intron , group ii intron , rna , chemistry , rna splicing , gene , organic chemistry
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 fromLactococcus lactis intoL. 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 theL. 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.