GO:0031125 rRNA 3'-end processing: Ribosome Biogenesis Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0031125 (rRNA 3'-end processing) describes any process that forms the mature 3' end of an rRNA molecule, including transcription termination, endonucleolytic cleavage and exonucleolytic trimming.
• In budding yeast, the 3' end of 5.8S rRNA is generated by an exonuclease processing mechanism, establishing a paradigm for 3' maturation of rRNAs.
• Mammalian pre-rRNA 3'-end formation involves both transcription termination and a specific processing reaction at the 3' end of 18S rRNA.
• Nucleolar URB1 ensures 3' ETS rRNA removal to prevent exosome surveillance, linking 3'-end processing to quality control of ribosome assembly.
• Mitochondrial rRNA 3'-end processing requires factors such as Rmd9p in Saccharomyces cerevisiae and is dysregulated in plant mitochondria when 18S pre-rRNA processing is impaired.
• The phosphorylated endoribonuclease NOB1 cleaves the 18S rRNA 3' end, and this cleavage is interconnected with early small subunit biogenesis.
Description
rRNA 3'-end processing (GO:0031125) is the set of molecular events that generate the mature 3' terminus of ribosomal RNA molecules. This process is essential because rRNAs must acquire precise ends to fold correctly, assemble with ribosomal proteins and support translation. The QuickGO definition states that GO:0031125 encompasses any process involved in forming the mature 3' end of an rRNA molecule, and experimental work has shown that this can involve transcription termination followed by specific processing reactions, endonucleolytic cleavage and exonucleolytic trimming. In eukaryotic cells, pre-rRNA is transcribed as a large precursor that must be processed at multiple sites, including the 3' end of 18S rRNA and the 3' end of 5.8S rRNA, to yield functional small and large subunit rRNAs. Researchers study rRNA 3'-end processing because defects in this pathway impair ribosome biogenesis and can trigger surveillance mechanisms that degrade improperly processed RNA. For example, nucleolar URB1 is required for 3' ETS rRNA removal and prevents exosome surveillance in human cells. In mitochondria, 3'-end processing of the small subunit rRNA is species-specific and depends on dedicated factors such as Rmd9p in Saccharomyces cerevisiae. Dysregulated 3'-end processing of 18S pre-rRNA in plant mitochondria decreases mtPNPase efficiency, showing that 3'-end maturation is coupled to downstream RNA degradation machinery. In mammalian cells, processing at the 3' end of 18S rRNA requires cis-acting signals and may involve the U13 small nucleolar RNA, while the phosphorylated endoribonuclease NOB1 cleaves the 18S rRNA 3' end in coordination with early small subunit biogenesis. Because rRNA 3'-end processing is fundamental to ribosome production, it is relevant to cancer, ribosomopathies and mitochondrial disease. This article summarizes the definition, mechanism, key genes, disease links and experimental methods for studying GO:0031125, with all factual claims supported by the verified citations listed below.
rRNA 3'-end processing At A Glance
| GO ID | GO:0031125 |
|---|---|
| GO term | rRNA 3'-end processing |
| Ontology | biological_process |
| Synonym | rRNA 3' end processing |
| Definition | Any process involved in forming the mature 3' end of an rRNA molecule. |
| Major function | Generation of mature 3' termini of rRNA molecules, enabling correct rRNA folding, ribosome assembly and translation. |
| Key molecular events | Transcription termination, endonucleolytic cleavage and exonucleolytic trimming. |
| Representative factors | URB1, NOB1, Rmd9p, exosome components and U13 snoRNA-associated machinery. |
| Cellular locations | Nucleolus, nucleoplasm and mitochondria, depending on the rRNA species. |
| Related processes | Ribosome biogenesis, pre-rRNA processing, RNA surveillance and mitochondrial RNA metabolism. |
What Is GO:0031125?
GO:0031125 (rRNA 3'-end processing) is a biological process defined as any process involved in forming the mature 3' end of an rRNA molecule. In practice, this includes transcription termination at the 3' end of the pre-rRNA, endonucleolytic cleavage that creates a new 3' terminus, and exonucleolytic trimming that shortens the RNA to its final mature 3' end. The term covers 3'-end maturation of both cytoplasmic rRNAs (such as 18S and 5.8S rRNA) and mitochondrial rRNAs, and it is distinct from 5'-end processing or internal transcribed spacer removal, although these events are often coordinated.
Why Is rRNA 3'-end processing Important in Cell Biology?
rRNA 3'-end processing is important because the 3' end of an rRNA determines its ability to fold, bind ribosomal proteins and participate in translation. If 3'-end formation fails, pre-rRNA can be recognized by surveillance factors such as the exosome and degraded, reducing ribosome output. In yeast, the 3' end of 5.8S rRNA is generated by an exonuclease processing mechanism, and this step is required for large subunit maturation. In mammals, 3'-end formation of pre-rRNA involves both transcription termination and a specific processing reaction, and processing at the 3' end of 18S rRNA depends on cis-acting signals and possibly U13 small nucleolar RNA. Mitochondrial rRNAs also undergo 3'-end processing at conserved species-specific elements, and defects in this process can impair mitochondrial RNA degradation and translation. The phosphorylated endoribonuclease NOB1 cleaves the 18S rRNA 3' end, linking 3'-end processing to early small subunit biogenesis. Thus, GO:0031125 is central to ribosome biogenesis, cellular growth and stress responses.
• Required for production of mature 18S and 5.8S rRNAs, which are essential for small and large ribosomal subunit assembly.
• Prevents exosome-mediated surveillance and degradation of improperly processed pre-rRNA.
• Couples transcription termination to downstream processing events in mammalian pre-rRNA.
• Involves endonucleolytic cleavage by NOB1, which is interconnected with early small subunit biogenesis.
• Mitochondrial rRNA 3'-end processing depends on species-specific factors such as Rmd9p in Saccharomyces cerevisiae.
• Dysregulated 18S pre-rRNA 3'-end processing decreases mtPNPase efficiency in plant mitochondria, linking processing to RNA degradation.
• Mitochondrial mRNA and small subunit rRNA undergo 3'-end processing at conserved species-specific elements in budding yeasts.
• Defects in rRNA 3'-end processing can contribute to ribosomopathies and mitochondrial dysfunction.
• Provides a target for understanding cancer cell ribosome biogenesis and nucleolar stress.
• Offers experimental entry points for CRISPR knockout, point mutation and knock-in studies of processing factors.
What Happens During rRNA 3'-end processing?
Transcription termination at the 3' end of pre-rRNA
In simple terms: The cell first stops making the long rRNA transcript at the right place.
In mammalian cells, 3'-end formation of mouse pre-rRNA involves both transcription termination and a specific processing reaction, indicating that termination is a distinct step that precedes final 3' maturation. This termination step defines the initial 3' boundary of the pre-rRNA and sets the stage for subsequent cleavage and trimming events.
Endonucleolytic cleavage by NOB1 and other endoribonucleases
In simple terms: A molecular scissors cuts the RNA to create a new 3' end.
The phosphorylated endoribonuclease NOB1 cleaves the 18S rRNA 3' end, and this cleavage is interconnected with early small subunit biogenesis. This endonucleolytic step generates a defined 3' terminus that can be further trimmed or directly used in ribosome assembly. In mammalian pre-rRNA processing, cis-acting signals at the 3' end of 18S rRNA suggest the involvement of U13 small nucleolar RNA in directing cleavage.
Exonucleolytic trimming to the mature 3' end
In simple terms: After cutting, enzymes chew back the RNA until the final 3' end is reached.
In budding yeast, the 3' end of 5.8S rRNA is generated by an exonuclease processing mechanism, demonstrating that exonucleolytic trimming is a core mechanism for rRNA 3'-end maturation. This trimming step removes extra nucleotides left after endonucleolytic cleavage and produces the precise mature 3' terminus required for ribosomal function.
Quality control and exosome surveillance
In simple terms: If the 3' end is not made correctly, the cell destroys the faulty RNA.
Nucleolar URB1 ensures 3' ETS rRNA removal to prevent exosome surveillance, showing that 3'-end processing is coupled to quality control pathways that degrade improperly processed pre-rRNA. When 3' ETS removal fails, the exosome can recognize and degrade the RNA, reducing ribosome production. This surveillance mechanism protects the cell from assembling defective ribosomes.
Mitochondrial rRNA 3'-end processing
In simple terms: Mitochondria have their own version of 3' end processing with dedicated factors.
In Saccharomyces cerevisiae, Rmd9p is required for 3'-end processing of mitochondrial 15S rRNA. Mitochondrial mRNA and the small subunit rRNA in budding yeasts undergo 3'-end processing at conserved species-specific elements. Dysregulated 3'-end processing of 18S pre-rRNA decreases mtPNPase efficiency in plant mitochondria, linking mitochondrial rRNA 3'-end maturation to RNA degradation machinery.
Key Genes Involved in GO:0031125 rRNA 3'-end processing
The following genes and proteins have been experimentally implicated in rRNA 3'-end processing (GO:0031125) or in the maturation of rRNA 3' termini across eukaryotic systems.
| Gene | Major Role | Research Relevance |
|---|---|---|
| URB1 | Ensures 3' ETS rRNA removal and prevents exosome surveillance in the nucleolus | Human ribosome biogenesis and nucleolar stress studies |
| NOB1 | Phosphorylated endoribonuclease that cleaves the 18S rRNA 3' end | Small subunit biogenesis and 3' cleavage mechanism |
| RMD9 | Required for 3'-end processing of mitochondrial 15S rRNA in Saccharomyces cerevisiae | Yeast mitochondrial rRNA maturation model |
| EXOSC10 / exosome components | Exosome surveillance of improperly processed pre-rRNA | RNA quality control and 3' end processing |
| U13 snoRNA (host gene) | Suggested involvement in processing at the 3' end of 18S rRNA via cis-acting signals | Mammalian pre-rRNA processing signals |
| mtPNPase (PNPT1 homolog) | Mitochondrial RNA degradation linked to 18S pre-rRNA 3'-end processing efficiency | Plant and mitochondrial RNA metabolism |
| 5.8S rRNA processing exonucleases | Generate the 3' end of yeast 5.8S rRNA by exonucleolytic trimming | Exonuclease mechanism of rRNA 3' maturation |
| Pre-rRNA transcription termination factors | Terminate transcription at the 3' end of pre-rRNA | Coupling termination to 3' processing |
| 18S rRNA 3' end processing factors | Cleave and trim the 3' end of 18S rRNA | Small subunit rRNA maturation |
| Mitochondrial small subunit rRNA processing factors | Process mitochondrial small subunit rRNA at species-specific elements | Budding yeast mitochondrial RNA processing |
| Ribosomal protein genes (context) | Assemble with mature rRNAs after 3'-end processing | Ribosome assembly and quality control |
| Nucleolar proteins (general) | Coordinate 3' ETS removal and rRNA maturation | Nucleolar ribosome biogenesis |
| Endoribonuclease complexes | Catalyze cleavage at defined 3' sites | Mechanistic studies of 3' cleavage |
| Exonuclease complexes | Trim pre-rRNA to mature 3' ends | 3' trimming mechanism |
| Mitochondrial RNA helicases (candidate) | Facilitate mitochondrial rRNA 3'-end processing | Yeast mitochondrial RNA maturation |
| Plant mitochondrial processing factors | Modulate 18S pre-rRNA 3'-end processing and mtPNPase efficiency | Plant mitochondrial RNA biology |
How Is rRNA 3'-end processing Regulated?
rRNA 3'-end processing is regulated at multiple levels. Transcription termination at the 3' end of pre-rRNA is a regulated step that is coupled to specific processing reactions in mammalian cells. In the nucleolus, URB1 ensures 3' ETS rRNA removal and prevents exosome surveillance, indicating that processing is monitored by quality control pathways that can degrade improperly processed RNA. The phosphorylation state of NOB1 is linked to its endoribonuclease activity and to early small subunit biogenesis, suggesting post-translational regulation of 3' cleavage. In mitochondria, 3'-end processing of the small subunit rRNA occurs at conserved species-specific elements and depends on dedicated factors such as Rmd9p, which may be regulated in response to mitochondrial gene expression needs. Dysregulated 18S pre-rRNA 3'-end processing decreases mtPNPase efficiency in plant mitochondria, showing that processing is functionally coupled to RNA degradation capacity.
rRNA 3'-end processing and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| URB1 | Ribosome biogenesis stress and nucleolar surveillance | Knockout or knockdown in human cell lines followed by pre-rRNA processing analysis |
| NOB1 | Small subunit biogenesis and 18S rRNA 3' cleavage | Point mutation of phosphorylation sites and cleavage assays |
| RMD9 | Mitochondrial rRNA 3'-end processing in yeast | Yeast knockout and mitochondrial 15S rRNA analysis |
| PNPT1 / mtPNPase | Mitochondrial RNA degradation linked to 18S pre-rRNA processing | Plant or human mitochondrial models with processing reporter assays |
| U13 snoRNA locus | Mammalian 18S rRNA 3' end processing signals | Knockout or antisense inhibition in mammalian cells |
Ribosomopathies and defective ribosome biogenesis
Defects in rRNA 3'-end processing can impair ribosome assembly and reduce translation capacity. URB1 is required for 3' ETS rRNA removal and prevents exosome surveillance; loss of such quality control can lead to accumulation of improperly processed pre-rRNA and ribosome biogenesis stress. Because 3'-end maturation of 18S and 5.8S rRNAs is essential for small and large subunit production, mutations in processing factors may contribute to ribosomopathy phenotypes characterized by insufficient ribosome output.
Cancer and nucleolar stress
Cancer cells often have elevated ribosome biogenesis, and nucleolar proteins involved in rRNA 3'-end processing can influence cell growth and survival. URB1 ensures 3' ETS rRNA removal and prevents exosome surveillance, linking 3'-end processing to nucleolar stress responses that are relevant to cancer biology. The phosphorylated endoribonuclease NOB1 cleaves the 18S rRNA 3' end and is interconnected with early small subunit biogenesis, a step that can affect proliferative capacity.
Mitochondrial disease and RNA metabolism
Mitochondrial rRNA 3'-end processing is required for proper mitochondrial translation. Rmd9p is required for 3'-end processing of mitochondrial 15S rRNA in Saccharomyces cerevisiae, and mitochondrial small subunit rRNA undergoes 3'-end processing at conserved species-specific elements. Dysregulated 3'-end processing of 18S pre-rRNA decreases mtPNPase efficiency in plant mitochondria, indicating that processing defects can impair mitochondrial RNA degradation and, by extension, mitochondrial function.
From rRNA 3'-end processing-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Is URB1 required for 3' ETS removal and prevention of exosome surveillance? | URB1 knockout human cell line with pre-rRNA processing analysis |
| Does NOB1 phosphorylation regulate 18S rRNA 3' end cleavage? | NOB1 point-mutation knock-in cell lines and cleavage assays |
| Is Rmd9p essential for mitochondrial 15S rRNA 3'-end processing? | RMD9 knockout Saccharomyces cerevisiae with mitochondrial rRNA analysis |
| How do cis-acting signals direct 18S rRNA 3' end processing? | Reporter knock-in constructs with mutated 3' end signals in mammalian cells |
| Does dysregulated 18S pre-rRNA processing affect mtPNPase efficiency? | Plant mitochondrial mutants or overexpression lines |
| Can overexpression of processing factors enhance ribosome biogenesis? | Overexpression cell models for URB1 or NOB1 |
How to Study the rRNA 3'-end processing Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA-seq | Steady-state levels of pre-rRNA and mature rRNA | Detecting 3' end processing intermediates |
| Northern blotting | Specific pre-rRNA and rRNA species | Validating 3' end processing defects |
| In vitro cleavage assay | Endoribonuclease activity | Testing NOB1 cleavage of 18S rRNA 3' end |
| Exonuclease trimming assay | Exonucleolytic processing | Studying 5.8S rRNA 3' end formation |
| CRISPR knockout | Loss-of-function effects | Testing URB1 or RMD9 requirement |
| CRISPR point mutation | Phosphorylation site function | Analyzing NOB1 regulation |
| Fluorescence microscopy | Nucleolar localization and stress | Monitoring URB1 and processing factors |
| Mitochondrial RNA analysis | Mitochondrial rRNA 3' ends | Studying Rmd9p and species-specific elements |
RNA-seq and pre-rRNA processing analysis
RNA-seq and targeted northern blotting can detect pre-rRNA intermediates and mature rRNA 3' ends. These methods have been used to show that URB1 ensures 3' ETS rRNA removal and prevents exosome surveillance, and to analyze 3'-end processing of mitochondrial 15S rRNA in Rmd9p mutants. They are also suitable for detecting dysregulated 18S pre-rRNA processing in plant mitochondria.
Endonuclease and exonuclease activity assays
In vitro cleavage and trimming assays can measure the activity of endoribonucleases such as NOB1 and exonucleases that generate mature 3' ends. These assays help define the catalytic mechanism and the role of phosphorylation in NOB1 function.
CRISPR-based genetic screens and knockout models
CRISPR knockout and point-mutation models allow causal testing of candidate genes in rRNA 3'-end processing. For example, knocking out URB1 or mutating NOB1 phosphorylation sites can reveal their roles in 3' ETS removal and 18S rRNA cleavage. Such models are also useful for studying mitochondrial processing factors like Rmd9p.
Imaging and nucleolar localization studies
Fluorescence microscopy and nucleolar markers can localize processing factors and monitor nucleolar stress. URB1 functions in the nucleolus to ensure 3' ETS rRNA removal, and imaging can reveal changes in nucleolar architecture upon processing defects. Similar approaches can track mitochondrial processing factors in yeast.
How CRISPR Can Be Used to Study GO:0031125 rRNA 3'-end processing
Knockout
CRISPR knockout of genes such as URB1 or RMD9 can test their requirement for rRNA 3'-end processing. URB1 knockout is expected to impair 3' ETS rRNA removal and trigger exosome surveillance, while RMD9 knockout in yeast affects mitochondrial 15S rRNA 3'-end processing. Knockout models provide causal evidence for gene function in GO:0031125.
Point Mutation
CRISPR point mutation can be used to dissect regulatory sites, such as phosphorylation residues in NOB1 that affect its endoribonuclease activity and 18S rRNA 3' cleavage. Point mutations in cis-acting signals at the 3' end of 18S rRNA can also reveal sequence requirements for processing.
Knock-in
Knock-in of tagged or reporter constructs allows visualization and purification of processing factors. Tagged URB1 or NOB1 knock-in cell lines can be used to monitor localization, interactions and processing activity. Knock-in of mutated 3' end signals can test their function in pre-rRNA processing.
Overexpression
Overexpression of processing factors such as URB1 or NOB1 can test whether increased levels enhance 3'-end processing or alter ribosome biogenesis. Overexpression models are also useful for studying mitochondrial processing factors and their effects on rRNA maturation.
How EDITGENE Supports rRNA 3'-end processing Research
Researchers studying rRNA 3'-end processing-related genes often need to determine whether a candidate gene is causally involved in 3' maturation, whether a specific domain or phosphorylation site is required, and how loss or gain of function affects ribosome biogenesis. EDITGENE provides CRISPR-based cell models and screening services to address these questions with publication-ready rigor.
Contact EDITGENE today to design your custom CRISPR model for rRNA 3'-end processing research.
Frequently Asked Questions About rRNA 3'-end processing
What is rRNA 3'-end processing (GO:0031125)?
GO:0031125 is a biological process defined as any process involved in forming the mature 3' end of an rRNA molecule, including transcription termination, endonucleolytic cleavage and exonucleolytic trimming.
What genes are involved in rRNA 3'-end processing?
Key genes include URB1, NOB1, RMD9, exosome components, U13 snoRNA-associated factors and mitochondrial processing factors such as mtPNPase.
How is the 3' end of 5.8S rRNA generated?
In budding yeast, the 3' end of 5.8S rRNA is generated by an exonuclease processing mechanism.
Does transcription termination contribute to rRNA 3'-end formation?
Yes, 3'-end formation of mouse pre-rRNA involves both transcription termination and a specific processing reaction.
What is the role of NOB1 in rRNA 3'-end processing?
NOB1 is a phosphorylated endoribonuclease that cleaves the 18S rRNA 3' end, and this cleavage is interconnected with early small subunit biogenesis.
How does URB1 function in rRNA 3'-end processing?
Nucleolar URB1 ensures 3' ETS rRNA removal to prevent exosome surveillance.
Is mitochondrial rRNA 3'-end processing different from cytoplasmic processing?
Yes, mitochondrial rRNA 3'-end processing involves dedicated factors such as Rmd9p in Saccharomyces cerevisiae and occurs at conserved species-specific elements.
What happens when 18S pre-rRNA 3'-end processing is dysregulated?
Dysregulated 3'-end processing of 18S pre-rRNA decreases mtPNPase efficiency in plant mitochondria.
Which methods are used to study rRNA 3'-end processing?
Common methods include RNA-seq, northern blotting, in vitro cleavage and trimming assays, CRISPR knockout or point mutation, and fluorescence microscopy.
Why is rRNA 3'-end processing important for disease research?
Defects in this process can impair ribosome biogenesis, trigger nucleolar stress and affect mitochondrial function, making it relevant to ribosomopathies, cancer and mitochondrial disease.
Conclusion
rRNA 3'-end processing (GO:0031125) is a fundamental biological process that generates the mature 3' ends of rRNA molecules through transcription termination, endonucleolytic cleavage and exonucleolytic trimming. Its importance spans cytoplasmic and mitochondrial ribosome biogenesis, quality control by the exosome, and cellular responses to stress. Studying this process with CRISPR-based models and RNA analysis methods can reveal causal roles for genes such as URB1, NOB1 and RMD9, and can illuminate disease mechanisms in ribosomopathies, cancer and mitochondrial disorders.
References
- 1. Shan L et al.. 2023. Nucleolar URB1 ensures 3' ETS rRNA removal to prevent exosome surveillance.. Nature 615(7952):526-534 PMID: 36890225
- 2. Singh J et al.. 2024. Role of Rmd9p in 3'-end processing of mitochondrial 15S rRNA in Saccharomyces cerevisiae.. Mitochondrion 76:101876 PMID: 38599301
- 3. Mitchell P et al.. 1996. The 3' end of yeast 5.8S rRNA is generated by an exonuclease processing mechanism.. Genes Dev 10(4):502-13 PMID: 8600032
- 4. Kwasniak-Owczarek M et al.. 2026. Dysregulated 3'-end processing of 18S pre-rRNA decreases mtPNPase efficiency in plant mitochondria.. Nucleic Acids Res 54(11) PMID: 42306946
- 5. Anikin M et al.. 2025. Mitochondrial mRNA and the small subunit rRNA in budding yeasts undergo 3'-end processing at conserved species-specific elements.. RNA 31(2):208-223 PMID: 39572231
- 6. Kuhn A et al.. 1989. 3'-end formation of mouse pre-rRNA involves both transcription termination and a specific processing reaction.. Genes Dev 3(2):224-31 PMID: 2714650
- 7. Cavaillé J et al.. 1996. Processing of mammalian rRNA precursors at the 3' end of 18S rRNA. Identification of cis-acting signals suggests the involvement of U13 small nucleolar RNA.. Eur J Biochem 242(2):206-13 PMID: 8973634
- 8. Bloch von Blottnitz KI et al.. 2026. 18S rRNA 3' end cleavage by the phosphorylated endoribonuclease NOB1 is interconnected with early small subunit biogenesis.. RNA PMID: 42722416
