TUT7

TUT7 (ZCCHC6/TENT3B) is a terminal uridylyl transferase that controls RNA fate by adding non-templated uridines to the 3' ends of small RNAs, mRNAs, and decay intermediates, acting redundantly with or independently of its paralog TUT4 depending on substrate (PMID:22898984, PMID:36071058). In let-7 biogenesis it operates through two structurally and kinetically distinct modes dictated by pre-miRNA 3'-overhang structure: distributive mono-uridylation of group II pre-miRNAs restores a canonical 2-nucleotide overhang to promote maturation, while oligo-uridylation of 3'-trimmed precursors marks them for degradation (PMID:25979828). Mode switching is governed by two functional modules—a catalytic module whose crystal structure reveals a duplex-RNA-binding pocket that orients group II pre-let-7 hairpins for mono-U addition, and a Lin28-interacting module that, engaged by the Lin28 ZK domain, forms a stable ternary complex enabling processive oligo-uridylation (PMID:28671666). TUT7 also recognizes a bipartite sequence motif to mono-uridylate a specific subset of mature miRNAs, with depletion shifting the 3' end toward mono-adenylation (PMID:25223788). Beyond miRNA control, TUT7 is the primary TUTase uridylating histone mRNA 3' ends and stem-loop degradation intermediates in cooperation with the 3'→5' exonuclease 3'hExo to drive complete histone mRNA decay (PMID:27609902, PMID:36041871), and it serves as a salvage decay enzyme acting with DIS3L2 to clear aberrant transcripts in FOCAD-deficient cells, where its loss is selectively lethal (PMID:39235218). Through targeted uridylation of specific mature miRNAs (miR-26b) and mRNAs (IL-6), TUT7 modulates inflammatory and tissue-remodeling gene expression and contributes to phenotypes including osteoarthritic cartilage damage (PMID:30302948).

1. 2012 High

   Established that TUT7 is a bona fide uridylyl transferase that, like TUT4, interacts with Lin28 to uridylate pre-let-7 and that the two enzymes redundantly control let-7 biogenesis, defining TUT7's founding role in the Lin28/let-7 axis.

   Evidence In vitro uridylation and reconstitution assays, domain-deletion mapping of a C2H2 zinc finger, and ES cell depletion

   PMID:22898984

   Open questions at the time

   • Did not resolve the structural basis of catalysis or substrate discrimination
   • Degree of substrate-specific division of labor between TUT4 and TUT7 left open
2. 2014 High

   Showed TUT7/TUT4 selectively mono-uridylate a defined subset of mature miRNAs via a bipartite sequence motif, revealing sequence-specific substrate recognition and an antagonism with 3' adenylation.

   Evidence In vitro motif-definition biochemistry, siRNA knockdown with deep sequencing, and zebrafish developmental perturbation

   PMID:25223788

   Open questions at the time

   • Did not establish how the motif is read structurally
   • Functional consequences of mono-U vs mono-A on individual miRNAs not fully resolved
3. 2015 High

   Resolved the mechanistic logic of TUT7 mode-switching, showing 3'-overhang structure dictates mono- versus oligo-uridylation and that, absent Lin28, both modes are distributive with overhang length controlling interaction frequency.

   Evidence In vitro uridylation assays, single-molecule experiments, and deep sequencing

   PMID:25979828

   Open questions at the time

   • Structural basis for overhang discrimination not yet visualized
   • How Lin28 converts distributive to processive activity left for later work
4. 2016 Medium

   Identified TUT7 as the primary TUTase uridylating histone mRNA 3' ends and stem-loop degradation intermediates, distinguishing it functionally from TUT4 and linking it to histone mRNA turnover with 3'hExo.

   Evidence siRNA knockdown of TUT7 and TUT4 with high-throughput sequencing of histone mRNAs

   PMID:27609902

   Open questions at the time

   • Knockdown rather than knockout; residual enzyme possible
   • Direct physical cooperation with 3'hExo not biochemically reconstituted here
5. 2017 High

   Defined the modular and structural basis of TUT7 activity by solving the catalytic module crystal structure in the mono-uridylation state and mapping a Lin28-interacting module required specifically for oligo-uridylation, explaining mode switching at atomic resolution.

   Evidence Crystal structure of the TUT7 catalytic module, domain mutagenesis, in vitro assays, and ternary complex reconstitution

   PMID:28671666

   Open questions at the time

   • No full-length structure including the LIM in the active oligo-U state
   • Structural transitions during processive synthesis not captured
6. 2017 Medium

   Connected TUT7 to innate immunity, showing macrophage TUT7 suppresses select cytokine responses to bacterial challenge, extending its role beyond RNA biogenesis into immune regulation.

   Evidence Zcchc6 knockout mice, intratracheal bacterial challenge, and macrophage stimulation assays

   PMID:28665939

   Open questions at the time

   • RNA substrate(s) mediating the cytokine phenotype not identified
   • Catalytic dependence of the immune effect not directly tested
7. 2019 High

   Demonstrated a dual mechanism by which TUT7 amplifies IL-6 expression—stabilizing the IL-6 transcript and uridylating miR-26b to relieve its repression of IL-6—and linked this to osteoarthritis pathology in vivo.

   Evidence Chondrocyte knockdown/overexpression, actinomycin D mRNA-stability chase, miRNA uridylation sequencing, and a surgical osteoarthritis KO mouse model with rescue

   PMID:30302948

   Open questions at the time

   • Mechanism by which miR-26b uridylation abrogates repression not detailed
   • Generality of TUT7-mediated mRNA stabilization beyond IL-6 unclear
8. 2022 High

   Using isogenic CRISPR knockouts, established the division of labor between TUT4 and TUT7—TUT4 drives bulk miRNA uridylation while TUT7 selectively controls specific miRNAs (miR-888 cluster)—and defined a uridylation-dependent miRNA set including let-7, miR-181b, and miR-222.

   Evidence CRISPR knockout of TENT2/TUT4/TUT7 alone and combined, deep sequencing, Northern blot, in vitro assays, and rescue

   PMID:36071058

   Open questions at the time

   • Basis for TUT7's selectivity toward specific miRNAs not mechanistically explained
   • Functional consequences for each dysregulated miRNA not all defined
9. 2022 High

   Confirmed via knockout that TUT7 uridylation of histone mRNA stem-loop degradation intermediates accelerates complete decay and that TUT7 cooperates with 3'hExo, which initiates trimming and sets 3'-end length.

   Evidence CRISPR knockout of TUT7 and 3'hExo, cell synchronization, and deep sequencing of degradation intermediates

   PMID:36041871

   Open questions at the time

   • Direct physical interaction and ordering of TUT7/3'hExo not structurally resolved
   • Downstream nuclease completing decay of uridylated intermediates not defined here
10. 2024 High

    Revealed a synthetic-lethal salvage RNA decay role in which FOCAD loss destabilizes the SKI complex and makes cells dependent on TUT7 (with DIS3L2) to clear aberrant RNA, nominating TUT7 as a selective cancer target and yielding first-in-class TUT4/7 inhibitors.

    Evidence CRISPR knockout epistasis (TUT7/TUT4/DIS3L2/FOCAD), functional genomics, FOCAD-reintroduction rescue, and small-molecule inhibitors with in vivo antiproliferative assays

    PMID:39235218

    Open questions at the time

    • Identity of the aberrant transcripts salvaged by TUT7 not enumerated
    • Mechanism rendering TUT7 non-redundant with TUT4 in this context unresolved
11. 2024 Low

    Proposed that TUT7 uridylates mature miR-1246 to promote its turnover, with SNRPB stabilization shaping exosomal miR-1246 levels that drive tumor-associated macrophage polarization and T cell suppression in colorectal cancer.

    Evidence Macrophage co-culture education system, TUT7 functional characterization, RNA-seq, and database mining

    PMID:38342611

    Open questions at the time

    • Mechanism described at abstract level without detailed TUT7-specific in vitro reconstitution
    • Direct enzymatic action on mature miR-1246 not biochemically isolated
    • SNRPB–TUT7 relationship not mechanistically defined
12. 2025 Medium

    Placed TUT7 within antiviral ZAP-mediated RNA decay, showing it uridylates the 5' KHNYN-cleavage fragment of viral RNA for DIS3L2 degradation and physically associates with ZAP and TRIM25 in an infection-enhanced, RNase-resistant manner.

    Evidence RNase-resistant co-immunoprecipitation, ordered pathway dissection, and ZMD reconstitution (preprint)

    PMID:bio_10.1101_2025.04.28.650959

    Open questions at the time

    • Preprint; not yet peer-reviewed
    • Structural basis of ZAP/TRIM25–TUT7 recruitment unresolved
    • Relative contributions of TUT4 vs TUT7 in ZMD not separated
13. 2025 Medium

    Extended TUT7's mRNA-destabilizing activity to MCPIP1, showing uridylation lowers MCPIP1 transcript stability and thereby modulates autophagy and fibrosis in pterygium fibroblasts.

    Evidence In vitro transcription/uridylation assays, co-IP, Western blot, qRT-PCR, and cellular migration/wound-healing assays

    PMID:40238115

    Open questions at the time

    • Single-lab study in a specialized cell context
    • Generality of TUT7-mediated mRNA destabilization across tissues unclear

• How TUT7 achieves substrate selectivity across its diverse RNA targets—miRNAs, histone mRNAs, mRNAs, and viral fragments—and what determines its non-redundant versus redundant relationship with TUT4 in each pathway remains unresolved.
• No unifying structural model explaining differential substrate engagement
• Cofactors/adaptors directing TUT7 to specific decay vs biogenesis pathways largely unmapped
• Full-length enzyme structure in oligo-uridylation state lacking