RBM26

RBM26 is a nuclear RNA-binding protein that functions as a limiting component of the PAXT (Poly(A) Tail eXosome Targeting) connection, coupling short polyadenylated nuclear RNA recognition to exosome-mediated degradation. Within PAXT, RBM26 (together with its paralog RBM27 and ZC3H3) is recruited to the 3′ ends of short nuclear RNAs, triggering conformational 'opening' of the co-transcriptionally loaded ZFC3H1 scaffold to license exosomal decay, thereby distinguishing short RNAs destined for degradation from longer transcripts routed to nuclear export (PMID:31950173, PMID:39461342). PABPN1 recruits RBM26/RBM27 to promote splicing of terminal introns harboring weak 3′ splice sites, linking RBM26 to pre-mRNA processing beyond RNA surveillance (PMID:37661812). In C. elegans, the RBM-26 ortholog directly binds mals-1 mRNA to negatively regulate the MALSU1 mitoribosomal assembly factor, and loss of RBM-26 causes mitochondrial dysfunction and axon degeneration (PMID:39480871).

1. 2012 Low

   Establishing RBM26 as a bona fide mRNA-binding protein resolved whether its predicted RNA-binding domains were functional in vivo.

   Evidence UV crosslinking and oligo(dT) interactome capture in HeLa cells identified RBM26 in the mRNA-bound proteome

   PMID:22658674

   Open questions at the time

   • Large-scale proteomics hit without functional follow-up specific to RBM26
   • RNA targets and binding specificity unknown
   • No mechanistic context for RBM26 function
2. 2017 Low

   Detection of mono-methylated arginine residues in RBM26 RG-repeat motifs indicated it is a substrate for arginine methyltransferases, raising the question of whether this modification regulates its RNA-binding or complex-assembly functions.

   Evidence Immunoprecipitation with MMA-specific antibody, mass spectrometry, and Western blot in EBV-transformed B cells

   PMID:28758620

   Open questions at the time

   • Single IP/MS identification with no functional follow-up of RBM26 methylation
   • Methyltransferase responsible not identified
   • Functional consequence of arginine methylation on RBM26 activity unknown
3. 2020 High

   Identification of RBM26 as a component of the PAXT connection answered where RBM26 operates within nuclear RNA surveillance and established it as a limiting factor for exosome-mediated polyadenylated RNA decay.

   Evidence Nuclear pA+-RNA proteome characterization, MTR4-ZFC3H1 complex purification, and siRNA knockdown showing PAXT substrate accumulation

   PMID:31950173

   Open questions at the time

   • Mechanism by which RBM26 recognizes or is recruited to PAXT substrates not defined
   • Whether RBM26 and RBM27 are redundant or have distinct substrate specificities unknown
   • Structural basis for RBM26 incorporation into the PAXT complex not determined
4. 2023 Medium

   Demonstrating that PABPN1 recruits RBM26/RBM27 to promote terminal intron splicing revealed a second function for RBM26 beyond RNA decay—connecting it to co-transcriptional splicing regulation.

   Evidence TurboID proximity labeling MS, co-immunoprecipitation, and splicing assays upon siRNA knockdown in HeLa cells

   PMID:37661812

   Open questions at the time

   • RBM26-specific interaction domains partly inferred from RBM27 mapping
   • Full spectrum of splicing events regulated by RBM26 not catalogued
   • Whether the splicing and PAXT functions of RBM26 are coordinated or independent is unclear
5. 2024 High

   Elucidation of ZFC3H1 conformational switching showed that RBM26/27 and ZC3H3 are recruited to 3′ ends of short nuclear RNAs to 'open' ZFC3H1, resolving how PAXT discriminates short RNAs for degradation from longer export-competent transcripts.

   Evidence Co-immunoprecipitation, RNA-seq, domain mutant analysis, and nascent RNA association assays in human cells

   PMID:39461342

   Open questions at the time

   • Precise RNA features that determine RBM26/27 recruitment to 3′ ends not defined
   • Whether RBM26 directly contacts ZFC3H1 or acts through ZC3H3 intermediary unclear
   • Structural basis of ZFC3H1 closed-to-open transition not resolved
6. 2024 High

   In C. elegans, RBM-26 directly binds mals-1 mRNA to suppress MALSU1 expression, and loss of this regulation causes mitochondrial dysfunction and axon degeneration—revealing a conserved in vivo role in post-transcriptional gene silencing with neurobiological consequences.

   Evidence C. elegans loss-of-function mutants, epistasis with mals-1 double mutants, biochemical RNA-binding screen, axon morphology assays

   PMID:39480871

   Open questions at the time

   • Whether human RBM26 similarly regulates MALSU1 mRNA not tested
   • Mechanism of mals-1 mRNA repression (degradation vs. translational silencing) not distinguished
   • Neuronal cell-type specificity and developmental timing of this regulation not fully characterized
7. 2025 Medium

   In fission yeast, the RBM26/27 ortholog Rmn1 interacts with Pab2/PABPN1 and the histone methyltransferase Clr4 and is essential for constitutive heterochromatin formation, suggesting an ancestral link between PAXT-related RNA surveillance and chromatin silencing.

   Evidence Genetic deletion, co-immunoprecipitation, and H3K9me ChIP at centromeres in S. japonicus

   PMID:40163528

   Open questions at the time

   • Findings in a distantly related yeast ortholog; conservation in mammals not established
   • Whether RBM26 contributes to heterochromatin in human cells untested
   • Mechanism by which Rmn1 bridges RNA processing to histone methylation not resolved

• Key unresolved questions include the structural basis for RBM26 integration into the PAXT complex, whether RBM26 and RBM27 have distinct or fully redundant substrate specificities, and whether the splicing, RNA decay, and potential chromatin functions of RBM26 are mechanistically coordinated.
• No high-resolution structure of RBM26 alone or in complex
• Functional distinction between RBM26 and RBM27 not established
• Integration of splicing and PAXT decay functions not investigated