Affinage

POP4

Ribonuclease P protein subunit p29 · UniProt O95707

Length
220 aa
Mass
25.4 kDa
Annotated
2026-04-28
15 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

POP4 (Rpp29) is a core protein subunit of the RNase P and RNase MRP ribonucleoprotein complexes that functions in tRNA processing and has acquired additional eukaryote-specific roles in chromatin regulation and DNA repair. Rpp29 adopts an OB-fold beta-barrel structure and heterodimerizes with Rpp21 through a coupled-folding mechanism; this binary complex binds the specificity domain (S-domain) of the RNase P RNA to activate pre-tRNA cleavage (PMID:14673079, PMID:19733182, PMID:18929577). In mammalian cells, Rpp29 directly interacts with histone H3.3 via a eukaryote-specific N-terminal extension and represses H3.3 nucleosome deposition at transcriptionally active genes, promoting heterochromatic histone modifications (PMID:26842893, PMID:29921582). Rpp29 is also recruited to DNA damage sites in a PARP1-dependent manner, binds poly(ADP-ribose), and facilitates homology-directed repair of double-strand breaks (PMID:28432356).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1999 Medium

    Establishing Rpp29 as a bona fide subunit of the active human RNase P holoenzyme resolved its identity as a functional component of this essential tRNA-processing ribonucleoprotein.

    Evidence Immunoprecipitation of catalytically active RNase P from HeLa cells using anti-Rpp29 antibodies

    PMID:10024167

    Open questions at the time
    • Single-lab immunoprecipitation without reciprocal validation from Rpp29 side
    • Stoichiometry and direct RNA contacts not determined
    • No functional assay of Rpp29 depletion on tRNA processing
  2. 2003 High

    Determination of the three-dimensional structure of archaeal Rpp29 as an OB-fold beta-barrel, combined with in vitro reconstitution showing its essentiality, provided the first structural framework for understanding how this subunit contributes to RNase P function.

    Evidence NMR structure determination of Mth Rpp29; reconstitution of archaeal RNase P holoenzyme; NMR chemical shift perturbation mapping RNA-binding surface

    PMID:14622001 PMID:14673079

    Open questions at the time
    • RNA-binding interface mapped at low resolution via chemical shift perturbation
    • Eukaryotic Rpp29 structure not yet determined
  3. 2004 High

    A high-resolution crystal structure identified two candidate RNA-binding sites on the Rpp29 OB-fold and revealed that strand β7 mediates intermolecular protein–protein contacts, delineating separate interaction surfaces for RNA and protein partners.

    Evidence X-ray crystallography of Ph1771p at 2.0 Å resolution

    PMID:15317976

    Open questions at the time
    • Functional validation of identified RNA-binding sites by mutagenesis not yet performed
    • Protein–protein interaction via β7 not confirmed in holoenzyme context
  4. 2008 High

    Crystal and NMR structures of the Rpp21–Rpp29 heterodimer revealed the molecular interface (Rpp21 N-terminal helices contacting Rpp29 N-terminal extension, β2, and C-terminal helix) and mutagenesis confirmed that heterodimerization is required for RNase P function.

    Evidence Crystal structure of PhoRpp21–PhoRpp29 complex; NMR structure of Pfu RPP21 with chemical shift perturbation mapping; mutational analysis

    PMID:18922021 PMID:18929577

    Open questions at the time
    • Whether the same interface is preserved in the eukaryotic heterodimer
    • How the heterodimer contacts the RNA in the assembled holoenzyme
  5. 2009 High

    NMR structure of the RPP21–RPP29 binary complex demonstrated that complex formation involves coupled protein folding, and enzymatic footprinting localized the pair to the S-domain of RNase P RNA, defining its site of action within the holoenzyme.

    Evidence Solution NMR of binary complex; enzymatic footprinting of RNase P RNA

    PMID:19733182

    Open questions at the time
    • Coupled folding characterized only in archaeal system
    • Precise nucleotide contacts within the S-domain not resolved
  6. 2010 Medium

    Chimeric RNA experiments functionally confirmed that the Rpp21–Rpp29 pair specifically stabilizes and activates the S-domain of RNase P RNA, distinguishing its role from the Pop5–Rpp30 pair that acts on the catalytic domain.

    Evidence Domain-swapped chimeric RNase P RNA cleavage assays in vitro

    PMID:20139629

    Open questions at the time
    • Chimeric approach performed only with archaeal components
    • Mechanism of S-domain activation (conformational change vs. substrate positioning) unknown
  7. 2012 Medium

    Thermodynamic dissection of RPP21–RPP29 binding established that coupled folding contributes a large excess heat capacity change, providing a quantitative biophysical framework for the heterodimerization mechanism.

    Evidence ITC across temperature, ionic strength, and pH ranges with a folding-deficient RPP21 mutant

    PMID:22243443

    Open questions at the time
    • Thermodynamic parameters measured only for archaeal proteins
    • How coupled folding is regulated in vivo not addressed
  8. 2016 Medium

    Discovery that Rpp29 is recruited to histone H3.3/RNA complexes at transcription sites and that its depletion increases H3.3 chromatin incorporation revealed an unexpected eukaryote-specific role for an RNase P subunit in chromatin regulation, distinct from tRNA processing.

    Evidence Live-cell imaging; siRNA knockdown with H3.3 chromatin incorporation assay in mammalian cells; pull-down and mutagenesis of archaeal Rpp21–Rpp29–RNA ternary complex

    PMID:26842893 PMID:27810361

    Open questions at the time
    • Whether H3.3 repression requires intact RNase P catalytic activity
    • Mechanism by which Rpp29 prevents H3.3 deposition not defined
    • Single-lab observation for chromatin function
  9. 2017 Medium

    Demonstration that Rpp29 is recruited to DNA damage sites in a PARP1-dependent manner, binds PAR, and is required specifically for homology-directed repair established a second non-canonical function for this RNase P subunit in genome maintenance.

    Evidence Laser microirradiation with live-cell imaging; siRNA knockdown with HDR/NHEJ reporter assays; PAR binding assays; PARP inhibitor experiments

    PMID:28432356

    Open questions at the time
    • Molecular mechanism linking Rpp29/PAR binding to HDR promotion unknown
    • Whether RNase P catalytic activity is required at damage sites unclear
    • Single-lab finding not independently replicated
  10. 2018 Medium

    Mapping the Rpp29–H3.3 interaction to a eukaryote-specific N-terminal extension of Rpp29 and showing that Rpp29 depletion derepresses euchromatic marks while reducing heterochromatic marks provided a molecular basis for how an RNase P subunit acquired chromatin-regulatory function.

    Evidence Recombinant protein binding assays; Rpp29 knockdown in KNS42 glioma cells with chromatin incorporation, RNA expression, and histone PTM analysis; oncogenic H3.3 mutant interaction assays

    PMID:29921582

    Open questions at the time
    • Whether Rpp29 acts directly on chromatin remodelers or through H3.3 sequestration
    • In vivo validation of N-terminal domain requirement not performed
    • Relevance to non-glioma cell types not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How Rpp29's canonical RNase P function and its non-canonical roles in chromatin regulation and DNA repair are coordinated within the same cell, and whether these activities are mediated by distinct Rpp29 pools or require intact RNase P catalytic activity, remains unresolved.
  • No structure of eukaryotic Rpp29 in the context of the human RNase P holoenzyme
  • Whether Rpp29's chromatin and DNA repair roles are RNase P RNA-dependent
  • No in vivo separation-of-function mutants distinguishing canonical from non-canonical roles

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 4 GO:0005198 structural molecule activity 3 GO:0042393 histone binding 2
Localization
GO:0005634 nucleus 3 GO:0005694 chromosome 2
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-4839726 Chromatin organization 2 R-HSA-73894 DNA Repair 1
Partners
H2BC1H3F3APARP1POP1RPP21
Complex memberships
RNase MRPRNase P

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 Rpp29 (human homolog of yeast Pop4p) is a protein subunit of human RNase P; antibodies against recombinant Rpp29 precipitate catalytically active RNase P from HeLa cells, establishing it as part of the active enzyme complex. Immunoprecipitation of catalytically active RNase P with polyclonal antibodies against recombinant Rpp29 RNA (New York, N.Y.) Medium 10024167
2003 The archaeal Rpp29 homolog (Mth Rpp29/Mth11) adopts an oligonucleotide/oligosaccharide binding (OB) fold with a beta-barrel core and flexible N- and C-terminal extensions; it is an essential protein component of the archaeal RNase P holoenzyme as shown by reconstitution experiments, and NMR chemical shift perturbation identified its RNA-binding interface with the full RNase P RNA subunit. Solution NMR structure determination; reconstitution of archaeal RNase P holoenzyme from recombinant components; NMR chemical shift perturbation with full RNA subunit Proceedings of the National Academy of Sciences of the United States of America High 14673079
2003 The archaeal Rpp29 homolog from Archaeoglobus fulgidus forms a six-stranded antiparallel beta-sheet structure with flexible N- and C-terminal tails; conserved surface residues in loop regions (beta2-beta3, beta4-beta5) and the flexible tails are likely RNA- and protein-interaction surfaces, consistent with the structural homology to Pop4p. Multidimensional NMR structure determination; amide proton exchange and 15N relaxation rate measurements Biochemistry Medium 14622001
2004 Crystal structure of the archaeal Rpp29 homolog Ph1771p at 2.0 Å resolution revealed an OB-fold beta-barrel with two potential RNA-binding sites: a concave surface with clustered positive charges and a loop region (beta2-beta3) with conserved hydrophilic residues that interact with sulfate ion; strand beta7 mediates protein-protein interactions via intermolecular antiparallel beta-sheet contacts. X-ray crystallography at 2.0 Å resolution; structural comparison RNA (New York, N.Y.) High 15317976
2008 The archaeal homologs of Rpp21 and Rpp29 (PhoRpp21 and PhoRpp29) form a heterodimer whose crystal structure shows that the two N-terminal helices of PhoRpp21 interact with the N-terminal extension, beta-strand beta2, and C-terminal helix of PhoRpp29 via hydrogen bonds and salt bridges; mutational analysis confirmed that heterodimerization is important for RNase P function, and the complex displays a positively charged RNA-binding surface. Crystal structure determination of PhoRpp21-PhoRpp29 complex; mutational analysis of interface residues Journal of molecular biology High 18929577
2008 Pyrococcus furiosus RPP21 adopts a structure consisting of two alpha-helices and a zinc-binding motif; NMR chemical shift perturbation showed that the primary contact surface of RPP21 with RPP29 is localized to its two helices. Solution NMR structure determination; NMR chemical shift perturbation Biochemistry High 18922021
2009 Solution NMR structure of the Pyrococcus furiosus RPP21-RPP29 binary complex showed that complex formation is accompanied by coupled protein folding; enzymatic footprinting localized the RPP21-RPP29 pair to the specificity domain (S-domain) of the RNase P RNA, defining its functional domain of action. Solution NMR structure of binary complex; enzymatic footprinting of RPR Journal of molecular biology High 19733182
2010 Functional chimeric RNase P RNA experiments demonstrated that PhoRpp21 and PhoRpp29 (archaeal homologs of Rpp21 and Rpp29) function in the stabilization/activation of the S-domain of the RNase P RNA, while PhoRpp30 and PhoPop5 function in the C-domain, defining the domain-specific roles of these protein pairs. Chimeric RNase P RNA assays with domain-swapped RNAs; in vitro cleavage assays Bioscience, biotechnology, and biochemistry Medium 20139629
2012 Isothermal titration calorimetry of archaeal RPP21-RPP29 interaction revealed that coupled protein folding contributes significantly to the excess negative heat capacity change (ΔCp) upon complex formation; a folding-deficient RPP21 point mutant confirmed the role of binding-coupled folding, and the interaction showed strong ionic strength and pH dependence. Isothermal titration calorimetry (ITC) over ranges of temperature, ionic strength, pH, with folding-deficient mutant Biochemistry Medium 22243443
2016 Rpp29 is recruited to a histone H3.3/RNA complex at transcription sites and Rpp29 knockdown increases H3.3 chromatin incorporation, demonstrating that Rpp29 represses histone H3.3 nucleosome deposition; POP1 and Rpp21 are similarly recruited, suggesting a variant RNase P regulates H3.3 chromatin assembly. Live-cell imaging of H3.3 complex; Rpp29 siRNA knockdown with H3.3 chromatin incorporation assay; colocalization experiments Molecular biology of the cell Medium 26842893
2016 Pull-down assay showed that PhoRpp21 binds directly to RNase P RNA (PhopRNA) and serves as the primary binding element, while PhoRpp29 alone has reduced affinity; mutational analysis identified Lys53, Lys54, Lys56 at the N-terminal helix of PhoRpp21 and the 10 C-terminal residues of PhoRpp29 as essential for PhopRNA activation; deletion of the loop linking P11-P12 helices in the PhopRNA S-domain impaired complex binding. Pull-down assay with recombinant proteins and RNA; mutational analysis of protein residues and RNA elements Biochemical and biophysical research communications Medium 27810361
2017 Rpp29 and Rpp21 are rapidly recruited to laser-microirradiated DNA damage sites in a PARP1-dependent manner, bind poly ADP-ribose (PAR) moieties, and their depletion impairs homology-directed repair (HDR) of double-strand breaks without affecting NHEJ; depletion of H1 RNA diminishes their recruitment, and RNase P activity is augmented after DNA damage in a PARP1-dependent manner. Laser microirradiation with live-cell imaging; siRNA knockdown with HDR/NHEJ reporter assays; PAR binding assays; PARP1 inhibitor experiments Scientific reports Medium 28432356
2018 Rpp29 interacts with histone H3.3 through a sequence element in its own N-terminus (absent in archaeal Rpp29), and with histone H2B at an adjacent site; Rpp29 represses H3.3 incorporation into transcriptionally active genes, represses mRNA and antisense RNA expression, and promotes heterochromatic PTMs (H3K9me3, H3K27me3) while repressing euchromatic PTMs; oncogenic H3.3 mutations alter the H3.3-Rpp29 interaction. Biochemical binding assay with recombinant proteins; Rpp29 KD in KNS42 glioma cells with chromatin incorporation, RNA expression, and histone PTM readouts; mutational analysis The Journal of biological chemistry Medium 29921582

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1999 Rpp14 and Rpp29, two protein subunits of human ribonuclease P. RNA (New York, N.Y.) 48 10024167
2003 Structure of Mth11/Mth Rpp29, an essential protein subunit of archaeal and eukaryotic RNase P. Proceedings of the National Academy of Sciences of the United States of America 40 14673079
2009 Solution structure of an archaeal RNase P binary protein complex: formation of the 30-kDa complex between Pyrococcus furiosus RPP21 and RPP29 is accompanied by coupled protein folding and highlights critical features for protein-protein and protein-RNA interactions. Journal of molecular biology 34 19733182
2008 Structure of an archaeal homolog of the human protein complex Rpp21-Rpp29 that is a key core component for the assembly of active ribonuclease P. Journal of molecular biology 34 18929577
2004 Crystal structure of archaeal ribonuclease P protein Ph1771p from Pyrococcus horikoshii OT3: an archaeal homolog of eukaryotic ribonuclease P protein Rpp29. RNA (New York, N.Y.) 32 15317976
2003 NMR structure of an archaeal homologue of ribonuclease P protein Rpp29. Biochemistry 26 14622001
2017 A role of human RNase P subunits, Rpp29 and Rpp21, in homology directed-repair of double-strand breaks. Scientific reports 25 28432356
2016 RNase P protein subunit Rpp29 represses histone H3.3 nucleosome deposition. Molecular biology of the cell 24 26842893
2008 Solution structure of Pyrococcus furiosus RPP21, a component of the archaeal RNase P holoenzyme, and interactions with its RPP29 protein partner. Biochemistry 19 18922021
2010 Archaeal homologs of human RNase P protein pairs Pop5 with Rpp30 and Rpp21 with Rpp29 work on distinct functional domains of the RNA subunit. Bioscience, biotechnology, and biochemistry 18 20139629
2018 Rpp29 regulates histone H3.3 chromatin assembly through transcriptional mechanisms. The Journal of biological chemistry 16 29921582
2004 Inhibition of the expression of the human RNase P protein subunits Rpp21, Rpp25, Rpp29 by external guide sequences (EGSs) and siRNA. Journal of molecular biology 16 15351636
2012 Thermodynamics of coupled folding in the interaction of archaeal RNase P proteins RPP21 and RPP29. Biochemistry 9 22243443
2003 Preparation of uniformly labeled NMR samples in Escherichia coli under the tight control of the araBAD promoter: expression of an archaeal homolog of the RNase P Rpp29 protein. Protein expression and purification 8 12699688
2016 Functional characterization of archaeal homologs of human nuclear RNase P proteins Rpp21 and Rpp29 provides insights into the molecular basis of their cooperativity in catalysis. Biochemical and biophysical research communications 2 27810361