INTS5

INTS5 is a structural subunit of the Integrator complex that contributes to the 3' end processing of small nuclear RNAs and to Integrator-dependent transcriptional regulation at RNA Polymerase II (PMID:33548203, PMID:19605500). Within Integrator it nucleates a dedicated module, forming a stable subcomplex with INTS8 that is biochemically distinct from the INTS10/13/14 subcomplex and the INTS4/9/11 catalytic core (PMID:33548203); this module expands into an INTS5/8/10/15 assembly that cryo-EM and integrative modeling place within the fully assembled Integrator bound to the paused RNA Polymerase II elongation complex, defining INTS5's architectural role in Integrator organization (PMID:38823386). Functionally, loss of INTS5 disrupts U1 and U2 snRNA 3' end processing, which in zebrafish causes aberrant splicing of smad1 and smad5, reduced expression of the hematopoietic genes scl and gata1, and arrested erythroid differentiation, placing INTS5 upstream of BMP/Smad signaling in hematopoiesis (PMID:19605500). In Drosophila neuroblast lineages, intS5 binds thousands of genomic sites including the earmuff transcription factor locus and is required for earmuff expression, so that its loss leads to dedifferentiation of intermediate neural progenitors into ectopic neuroblasts (PMID:31018143).

1. 2009 Medium

   Established that INTS5 is functionally required for snRNA 3' end processing and links this activity to a developmental signaling and differentiation program, defining its biological role before its structural place in Integrator was known.

   Evidence Antisense morpholino knockdown in zebrafish with RT-PCR of snRNA processing and smad splicing and blood smear analysis

   PMID:19605500

   Open questions at the time

   • Morpholino knockdown not confirmed with a genetic null or rescue
   • Direct biochemical role of INTS5 in the processing reaction not defined
   • Mechanism linking snRNA processing defects to smad mis-splicing not resolved
2. 2019 Medium

   Extended INTS5 function to chromatin-associated transcriptional control by showing it binds specific loci and is required to maintain a transcription factor program that suppresses progenitor dedifferentiation.

   Evidence Drosophila loss-of-function and INP-specific RNAi, cell-type-specific DamID, and genetic interaction analysis

   PMID:31018143

   Open questions at the time

   • Whether INTS5 acts at earmuff through snRNA processing or direct transcriptional regulation is unresolved
   • Single Drosophila ortholog system; human relevance not directly tested
   • Direct versus indirect nature of the 1413 binding sites not dissected
3. 2021 High

   Defined INTS5 as a discrete structural module of Integrator, showing it pairs with INTS8 as a subcomplex separate from the catalytic core and other peripheral modules.

   Evidence Biochemical fractionation and subcomplex reconstitution with cryo-EM of the catalytic core

   PMID:33548203

   Open questions at the time

   • Functional contribution of the INTS5/8 module to catalysis not assigned
   • How the module contacts the catalytic core within intact Integrator not yet shown
4. 2024 High

   Resolved the architectural role of INTS5 by placing the INTS5/8/10/15 subcomplex within fully assembled Integrator bound to paused RNA Pol II.

   Evidence Cryo-EM of the INTS5/8/10/15 subcomplex and integrative modeling of the full Integrator-paused elongation complex

   PMID:38823386

   Open questions at the time

   • Functional consequence of INTS5 positioning for cleavage or termination not directly tested
   • Dynamics of module engagement with the paused polymerase not captured

• How INTS5's structural position within Integrator mechanistically enables snRNA 3' end processing and locus-specific transcriptional control across species remains unresolved.
• No direct enzymatic or biochemical activity assigned to INTS5 itself
• Link between the structural module and the developmental phenotypes not mechanistically bridged