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Transcriptome-Wide Profiling of Protein-RNA Interactions by Cross-Linking and Immunoprecipitation Mediated by FLAG-Biotin Tandem Purification
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Mechanistic insights into Lin28-dependent oligo-uridylylation of pre-let-7 by TUT4

Xiaojie Han1, Seisuke Yamashita1, Kozo Tomita1

  • 1Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.

Nucleic Acids Research
|January 12, 2026
PubMed

Insights

Lin28 and TUT4/7 enzymes add uridines to pre-let-7 RNA, blocking its maturation. This study reveals the structure of this complex, showing how TUT4/7

Area of Science:

  • Molecular Biology
  • RNA Biology
  • Structural Biology

Background:

  • Lin28 proteins regulate gene expression by inhibiting microRNA biogenesis.
  • Terminal uridylyltransferases 4 and 7 (TUT4/7) add uridine tails to precursor let-7 (pre-let-7) RNA.
  • This oligo-uridylylation by TUT4/7 blocks Dicer processing, impacting cell differentiation and proliferation.

Purpose of the Study:

  • To elucidate the structural mechanism of Lin28-dependent pre-let-7 oligo-uridylylation by TUT4.
  • To understand how the TUT4 catalytic module (CM) and Lin28-interacting module (LIM) cooperate in this process.

Main Methods:

  • Cryogenic electron microscopy (cryo-EM) to determine the structure of the human TUT4 complex with Lin28A and oligo-uridylated pre-let-7.
  • Biochemical analyses to investigate the functional roles of different complex components.

Main Results:

  • The cryo-EM structure captured the elongation stage of pre-let-7 oligo-uridylylation.
  • Lin28A recruits pre-let-7 to the TUT4 LIM, facilitating CM association via protein-protein interactions.
  • The CM and LIM stabilize the double-stranded stem of pre-let-7, positioning its 3' end in the catalytic site for processive uridine tail elongation.

Conclusions:

  • The TUT4 LIM acts as a stable anchor, cooperating with Lin28A to ensure efficient and processive oligo-uridylylation of pre-let-7.
  • This structural insight provides a mechanistic understanding of how Lin28-TUT4 interaction regulates let-7 biogenesis and downstream cellular processes.

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