| Pre-mRNA Processing Factor 3 | |
|---|---|
| Gene Symbol | PRPF3 |
| Full Name | Pre-mRNA Processing Factor 3 |
| Aliases | HPRPF3, Prp3, Spliceosome component PRP3 |
| Chromosome | 1q21.1 |
| NCBI Gene ID | [9129](https://www.ncbi.nlm.nih.gov/gene/9129) |
| OMIM | [607444](https://www.omim.org/entry/607444) |
| Ensembl ID | ENSG00000148408 |
| UniProt ID | [O43371](https://www.uniprot.org/uniprot/O43371) |
| Protein Class | Splicing factor, U4/U6.U5 tri-snRNP component |
| Associated Diseases | [Retinitis Pigmentosa](/diseases/retinitis-pigmentosa), [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis), [Spinal Muscular Atrophy](/diseases/spinal-muscular-atrophy) |
PRPF3 encodes Pre-mRNA Processing Factor 3, also known as PRP3 or HPRPF3, a core component of the U4/U6.U5 tri-snRNP complex that catalyzes pre-mRNA splicing. This essential splicing factor plays a pivotal role in the removal of introns from precursor messenger RNAs, a fundamental step in eukaryotic gene expression. Located on chromosome 1q21.1, the PRPF3 gene produces a protein of 683 amino acids with a molecular weight of approximately 75 kDa.
The spliceosome, a large ribonucleoprotein complex composed of five small nuclear RNAs (U1, U2, U4, U5, and U6) and numerous associated proteins, executes the intricate process of pre-mRNA splicing. PRPF3 is specifically incorporated into the U4/U6.U5 tri-snRNP, the catalytic core of the spliceosome that performs the two transesterification reactions required for intron removal. The protein functions as an essential scaffold, maintaining the structural integrity of the tri-snRNP and facilitating its assembly into the active spliceosome.
Mutations in PRPF3 are causally linked to autosomal dominant retinitis pigmentosa (ADRP), a progressive inherited retinal degeneration leading to night blindness, visual field constriction, and eventually complete blindness. PRPF3-related retinopathy accounts for approximately 2-3% of ADRP cases, establishing this splicing factor as critical for photoreceptor survival and function. Beyond retinal disease, emerging evidence implicates PRPF3 dysfunction in neurodegenerative disorders including amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), where defective RNA processing contributes to motor neuron degeneration.
The PRPF3 gene spans approximately 18 kb on chromosome 1q21.1 and consists of 16 exons. The gene exhibits a typical eukaryotic structure with a TATA-less promoter containing multiple transcription initiation sites. The genomic architecture includes conserved splice sites and regulatory elements that ensure proper expression in various tissues.
The PRPF3 locus is located within a gene-rich region of chromosome 1, adjacent to several other genes involved in RNA processing and cellular metabolism. This genomic context suggests potential co-regulation with neighboring genes, although PRPF3 has distinct expression patterns that reflect its specialized functions in different cell types.
The PRPF3 protein possesses a multidomain architecture essential for its function within the spliceosome:
| Domain | Position | Function |
|---|---|---|
| N-terminal domain (1-150) | Coiled-coil region | Protein-protein interactions, tri-snRNP assembly |
| Central domain (150-400) | WD40-like repeats | Scaffolding, interaction with other splicing factors |
| C-terminal domain (400-683) | Helical regions | U4/U6 binding, catalytic core stabilization |
N-terminal coiled-coil region: Mediates homodimerization and interactions with other tri-snRNP components, particularly PRPF31. This region is critical for the proper assembly of the U4/U6.U5 complex.
Central WD40-like domain: Provides structural support and serves as an interaction platform for additional spliceosomal components. This domain mediates contacts with PRPF4 and other core tri-snRNP proteins.
C-terminal helical domain: Directly interacts with U4 and U6 snRNAs, stabilizing the snRNA components within the tri-snRNP. This region also participates in spliceosome activation.
The protein's architecture reflects its dual role as both a structural component of the tri-snRNP and a functional participant in the splicing reaction.
Within the spliceosome, PRPF3 is specifically localized to the U4/U6.U5 tri-snRNP:
Pre-mRNA splicing is a critical step in eukaryotic gene expression that removes non-coding introns and joins coding exons to produce mature messenger RNA. This process occurs within the spliceosome, a dynamic ribonucleoprotein machine that undergoes dramatic conformational changes during the splicing cycle.
The splicing reaction proceeds through two sequential transesterification steps:
First step (branch point): The 2' hydroxyl of an adenosine residue at the branch point attacks the 5' splice site, generating a lariat intermediate and freeing the 5' exon.
Second step (exon ligation): The 3' hydroxyl of the 5' exon attacks the 3' splice site, ligating the exons and releasing the intron lariat.
These reactions require the coordinated action of the spliceosome's catalytic components, including the RNA components (snRNAs) that provide catalytic activity and the protein components that facilitate substrate positioning and catalysis.
PRPF3 plays essential roles in the assembly and function of the U4/U6.U5 tri-snRNP:
Assembly pathway:
Once incorporated into the spliceosome, PRPF3 participates in the activation process that converts the pre-catalytic spliceosome into an active complex:
The essential nature of PRPF3 is underscored by the fact that its depletion leads to complete loss of splicing activity and cell death.
PRPF3 contributes to the fidelity of splice site recognition through multiple mechanisms:
PRPF3 is expressed ubiquitously in human tissues, reflecting its essential role in basic cellular functions:
| Tissue | Expression Level | Significance |
|---|---|---|
| Retina | Very High | Photoreceptor function |
| Brain | High | Neuronal RNA processing |
| Spinal Cord | High | Motor neuron function |
| Heart | High | Cardiac muscle splicing |
| Liver | Moderate | Hepatocyte function |
| Kidney | Moderate | Epithelial cell splicing |
| Lung | Moderate | Pulmonary function |
The high expression in retina and neural tissues reflects the particular demand for accurate RNA processing in these specialized cell types.
Within cells, PRPF3 exhibits a predominantly nuclear localization:
The nuclear localization reflects PRPF3's function in pre-mRNA processing, which occurs in the nucleus.
In the retina, PRPF3 is highly expressed in:
The high expression in photoreceptors explains why PRPF3 mutations primarily cause retinal degeneration rather than systemic disease.
Retinitis pigmentosa (RP) is a group of inherited retinal disorders characterized by progressive degeneration of rod photoreceptors, followed by cone photoreceptor loss. PRPF3 mutations cause autosomal dominant RP (ADRP), with over 15 pathogenic variants identified.
Pathogenic PRPF3 mutations (selected):
| Mutation | Effect | Frequency |
|---|---|---|
| T494K | Disrupts protein-protein interactions | Common |
| R565W | Impairs tri-snRNP assembly | Second hit |
| H390R | Affects U4/U6 binding | Rare |
| P496L | Disrupts splicing activity | Rare |
Mechanisms of photoreceptor degeneration:
Clinical phenotype:
ALS is a progressive neurodegenerative disease characterized by loss of upper and lower motor neurons. While PRPF3 is not a common cause of familial ALS, splicing factor dysfunction is increasingly recognized in disease pathogenesis.
Connections between PRPF3 and ALS:
The broader involvement of splicing factors in ALS highlights the importance of proper RNA metabolism for motor neuron survival.
SMA is an autosomal recessive neuromuscular disorder caused by deletions or mutations in the SMN1 gene, leading to motor neuron degeneration. While PRPF3 is not directly involved in SMA pathogenesis, the splicing machinery is fundamentally altered in this disease.
Links to PRPF3:
Alterations in splicing factors, including PRPF3, are observed in various cancers:
The relationship between splicing factors and cancer reflects the fundamental role of RNA processing in cellular homeostasis.
Therapeutic strategies for PRPF3-related RP include:
Gene therapy approaches:
Splicing modulation:
Neuroprotective strategies:
Cell-based therapies:
General approaches to address splicing dysfunction:
Potential biomarkers for splicing-related diseases:
Molecular approaches:
Cellular models:
Animal models:
Human studies:
PRPF3 interacts with multiple spliceosomal components:
| Interacting Protein | Interaction Type | Functional Significance |
|---|---|---|
| PRPF31 | Direct binding | Core tri-snRNP component |
| PRPF4 | Direct binding | Core tri-snRNP component |
| SNRNP200 | Direct binding | RNA helicase |
| U4 snRNA | Direct binding | snRNA component |
| U6 snRNA | Direct binding | snRNA component |
| U5 snRNA | Direct binding | snRNA component |
| Prp19 complex | Functional | Spliceosome activation |
| Splicing Factor | Gene | Function | Disease Associations |
|---|---|---|---|
| PRPF3 | PRPF3 | U4/U6.U5 tri-snRNP | RP, ALS |
| PRPF31 | PRPF31 | U4/U6.U5 tri-snRNP | RP |
| PRPF6 | PRPF6 | U5 snRNP | Cancer |
| PRPF8 | PRPF8 | Catalytic core | Cancer |
| PRPF4 | PRPF4 | Tri-snRNP assembly | RP |
PRPF3 encodes Pre-mRNA Processing Factor 3, an essential component of the U4/U6.U5 tri-snRNP complex that catalyzes pre-mRNA splicing. This splicing factor is critical for the removal of introns from precursor messenger RNAs, a fundamental step in eukaryotic gene expression that is particularly important in tissues with high RNA processing demands such as the retina and nervous system.
Mutations in PRPF3 cause autosomal dominant retinitis pigmentosa, accounting for a significant fraction of inherited retinal degenerations. The disease mechanism involves reduced splicing efficiency, leading to accumulation of unspliced pre-mRNAs and activation of stress pathways that ultimately result in photoreceptor apoptosis. The selective vulnerability of photoreceptors to PRPF3 dysfunction reflects the high demand for RNA processing in these specialized cells.
Beyond retinal disease, PRPF3 and other splicing factors are implicated in neurodegenerative disorders including ALS and SMA, where RNA processing defects contribute to neuronal dysfunction and death. Understanding PRPF3's role in splicing and disease provides insights into fundamental cellular biology and offers potential therapeutic strategies for treating splicing-related disorders.