PRPF3 (Pre-mRNA Processing Factor 3) is a core component of the U4/U5/U6 tri-snRNP complex within the spliceosome, the molecular machine responsible for removing introns from pre-mRNA. This 683-amino acid protein (approximately 77.8 kDa) is essential for catalytic spliceosome assembly and function. Mutations in PRPF3 are a well-established cause of autosomal dominant retinitis pigmentosa (ADRP), making it one of the most frequently mutated spliceosomal proteins in inherited retinal diseases. Beyond its role in the retina, PRPF3 is expressed throughout the central nervous system where it participates in neuronal splicing regulation, and dysfunction of this and other splicing factors has been implicated in various neurodegenerative diseases.
| Protein Name | Pre-mRNA Processing Factor 3 |
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| Gene Symbol | [PRPF3](/genes/prpf3) |
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| UniProt ID | [O43371](https://www.uniprot.org/uniprotkb/O43371/entry) |
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| Molecular Weight | 77.8 kDa (683 aa) |
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| Subcellular Localization | Nucleus (spliceosome) |
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| Expression | Ubiquitous, high in retina and brain |
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| Protein Family | Prp3 family (U4/U5/U6 tri-snRNP) |
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| PDB Structure | 5GM6, 6EXN |
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| Chromosome Location | 6q24.1 |
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| Protein Class | Splicing factor, WD repeat protein |
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PRPF3 possesses a characteristic domain architecture critical for its function in the spliceosome:
¶ Domain Organization
- N-terminal domain: Contains multiple WD repeat sequences that mediate protein-protein interactions within the tri-snRNP complex. The N-terminal region spans approximately residues 1-300 and contains six complete WD40 repeats that form the primary interaction surface.
- Middle region: Forms the core interaction surface with other tri-snRNP components, including direct contacts with PRPF31 and PRPF4. This region (residues 300-500) serves as the central hub for complex assembly.
- C-terminal domain: Participates in spliceosome activation and catalytic steps. The C-terminal region (residues 500-683) contains additional regulatory elements and post-translational modification sites.
The PRPF3 protein contains multiple WD40 repeat motifs that adopt a β-propeller fold, creating a platform for interactions with other spliceosomal proteins. The WD40 repeats form seven blades arranged in a circular β-propeller structure, enabling simultaneous interaction with multiple partner proteins including PRPF31, PRPF4, and SPAG1. Structural studies of the U4/U5/U6 tri-snRNP have revealed that PRPF3 sits at a central position, bridging interactions between the U4 snRNA and other protein components.
The β-propeller structure provides a large, relatively flat surface for protein-protein interactions, and mutations affecting this surface are commonly pathogenic. Several disease-causing mutations map directly to residues forming the interaction interface, disrupting complex formation without affecting overall protein folding.
Cryo-EM structures of the spliceosome have revealed the detailed architecture of PRPF3 within the tri-snRNP:
- Central position: PRPF3 forms the structural core of the particle
- U4 snRNA contacts: Direct interactions with U4 snRNA stabilize the RNA-protein complex
- Prp3-Prp31 interface: Critical for tri-snRNP stability
- Prp4 interaction: Connects to the U4 snRNA-specific helicase complex
PRPF3 undergoes several post-translational modifications that regulate its function:
- Phosphorylation: Multiple serine/threonine phosphorylation sites affect spliceosome assembly and disassembly. Casein kinase 2 (CK2) phosphorylation has been reported, potentially regulating spliceosome dynamics.
- Sumoylation: Reported sumoylation may regulate protein-protein interactions and subcellular localization. SUMO conjugation may target PRPF3 during stress conditions.
- Acetylation: Lysine acetylation influences subcellular localization and stability. Acetylation may affect the interaction with other spliceosomal components.
PRPF3 is one of seven "PRPF" proteins that form the core of the U4/U5/U6 tri-snRNP particle:
- U4 snRNA binding: PRPF3 interacts with U4 small nuclear RNA, forming the backbone of the tri-snRNP
- Complex stability: PRPF3, together with PRPF4 and PRPF31, stabilizes the U4 snRNA-U4/U6 duplex structure
- Catalytic core formation: The tri-snRNP is the catalytic core of the spliceosome
The splicing reaction proceeds through distinct stages:
- E complex: Recognition of the 5' splice site and branch point
- A complex (prespliceosome): Addition of U1 and U2 snRNPs
- B complex: Recruitment of the U4/U5/U6 tri-snRNP
- B complex (activated)*: Catalytic activation
- C complex (catalytic): Two transesterification reactions
- Post-catalytic complex: Disassembly and recycling
PRPF3 is essential for the transition from the B to B* complex, where the spliceosome becomes catalytically active.
PRPF3 participates in the regulation of tissue-specific alternative splicing:
- Retina: Required for proper splicing of photoreceptor-specific transcripts
- Brain: Regulates neuronal isoform expression
- Cell type-specific functions: Different neuronal populations show distinct PRPF3-dependent splicing patterns
Beyond canonical splicing, PRPF3 contributes to:
- mRNA quality control: Nonsense-mediated decay coupling
- Transcriptional coupling: Interactions with transcription machinery
- RNA processing homeostasis: Coordinating multiple RNA processing events
PRPF3 mutations are among the most common causes of autosomal dominant retinitis pigmentosa (ADRP), accounting for approximately 5-8% of all ADRP cases:
- Haploinsufficiency: Most disease-causing mutations result in reduced PRPF3 levels
- Photoreceptor vulnerability: Rod photoreceptors are particularly sensitive to PRPF3 deficiency
- Splicing defects: Aberrant splicing of essential photoreceptor genes
- Progressive degeneration: Initial rod degeneration followed by cone loss
- Night blindness: Usually the first symptom
- Tunnel vision: Progressive visual field constriction
- Color vision defects: Later-stage cone involvement
- Legal blindness: Typically by middle age
Over 30 pathogenic variants have been identified in PRPF3:
- Missense mutations: Often in WD40 repeat domains
- Splice-site mutations: Cause exon skipping or intron retention
- Nonsense mutations: Create premature termination codons
- p.Pro337Leu: Most common mutation, associated with relatively mild disease
- p.Arg542Cys: Severe early-onset disease
- Splice-site mutations: Variable severity depending on affected exon
While PRPF3 mutations primarily cause retinal degeneration, the protein is relevant to broader neurodegenerative processes:
- Splicing dysregulation: Altered splicing of APP and tau transcripts
- Spliceosome changes: Defective splicing machinery in AD brain
- PRPF3 expression: Reduced levels in AD temporal cortex
- Splicing factor involvement: Several splicing factors are dysregulated in PD
- α-synuclein splicing: Potential PRPF3 involvement in α-synuclein transcript regulation
- Mitochondrial splicing: Links to mitochondrial dysfunction in PD
- TDP-43 pathology: Spliceosome dysfunction in ALS
- RNA processing defects: Similar to other splicing factor diseases
- Motor neuron vulnerability: Possible PRPF3 involvement
PRPF3 mutations can cause:
- Leber congenital amaurosis: Severe early-onset disease
- Cone-rod dystrophy: Primarily cone involvement
- Foveal sparing RP: Retained central vision
- PRPF3 overexpression: AAV-mediated delivery of wild-type PRPF3
- Allele-specific silencing: Targeting mutant allele while preserving wild-type
- CRISPR correction: Precise genome editing of pathogenic variants
- Antisense oligonucleotides: Modulate splicing of PRPF3 or downstream targets
- Splice-switching oligonucleotides: Correct aberrant splicing patterns
- Small molecule modulators: Targeting spliceosome assembly
- Photoreceptor rescue: Neuroprotective compounds for rod survival
- Gene replacement: For null alleles
- Combination therapies: Multiple approaches for maximum benefit