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TitlePre-splicing conformation and stepwise circularization of a group I intron in Azoarcus pre-tRNA.
Journal, issue, pagesNat Commun, Year 2026
Publish dateMar 20, 2026
AuthorsYibao Hong / Jiashu Liu / Xiaojing Zhang / Ji Liu / Shanshan Li / Kaiming Zhang /
PubMed AbstractGroup I introns are catalytic RNAs capable of self-splicing, yet structural insights into full-length precursor RNAs and post-splicing circularization have been limited. Here, we present cryo-EM ...Group I introns are catalytic RNAs capable of self-splicing, yet structural insights into full-length precursor RNAs and post-splicing circularization have been limited. Here, we present cryo-EM structures of the Azoarcus pre-tRNA system across key catalytic stages, including the full-length precursor in Pre-1S conformations, the linear intron, and the circular introns, at 2.8-3.3 Å resolution. These structures reveal a preformed P1 helix, register shifts during splicing, and a conformational flip of G37 that stabilizes the circularization site. Biochemical analyses confirm a two-step circularization mechanism, generating a secondary circular product via an alternative ligation site. Together, our results provide an atomic-level view of a group I intron system through splicing and circularization. This work uncovers structural principles governing RNA conformational dynamics, catalysis, and circular RNA formation, with broad implications for ribozyme engineering.
External linksNat Commun / PubMed:41862486
MethodsEM (single particle)
Resolution2.86 - 3.27 Å
Structure data

64818

9v7n

EMDB-64818, PDB-9v7n:
Cryo-EM structures of the Azoarcus pre-tRNA(ILE) conformation a undergoing the first-step self-splicing
Method: EM (single particle) / Resolution: 3.11 Å

64819

9v7o

EMDB-64819, PDB-9v7o:
Cryo-EM structures of the Azoarcus pre-tRNA(ILE) conformation b undergoing the first-step self-splicing
Method: EM (single particle) / Resolution: 3.06 Å

64820

9v7p

EMDB-64820, PDB-9v7p:
Cryo-EM structures of the Azoarcus pre-tRNA(ILE) intron conformation after the self-splicing
Method: EM (single particle) / Resolution: 3.01 Å

64821

9v7q

EMDB-64821, PDB-9v7q:
Cryo-EM structures of the Azoarcus pre-tRNA(ILE) intron conformation after the cyclization
Method: EM (single particle) / Resolution: 3.27 Å

66618

9x6b

EMDB-66618, PDB-9x6b:
Cryo-EM structure of the Azoarcus sp. BH72 pre-tRNA(ILE) intron after second-step cyclization (circular form)
Method: EM (single particle) / Resolution: 2.86 Å

Chemicals

ChemComp-GMP:
GUANOSINE

ChemComp-MG:
Unknown entry

Source
  • azoarcus olearius (bacteria)
KeywordsRNA / Azoarcus pre-tRNA(ILE) / self-splicing / pre-1S / RNA structure / circular intron / Azoarcus sp. BH72 pre-tRNA(ILE); second-step cyclization; c' intron

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