RNA Editing Enzymes: Organisms, Mechanisms, and Methods
By Dr. Zubair Khalid, DVM, MS, PhD ·
Introduction to RNA Editing and Enzymes
What is RNA Editing?
RNA editing is a post-transcriptional process that alters the nucleotide sequence of an RNA molecule after transcription but before or during translation. Unlike splicing, which removes introns and joins exons, RNA editing changes the identity of individual nucleotides—substituting one base for another, or inserting/deleting bases—thereby producing an RNA sequence that differs from the template DNA. This process can change codons, create or destroy splice sites, alter miRNA target sites, or modify the stability of the transcript.
The term "editing" was first used in the 1980s to describe the addition of uridines to mitochondrial mRNAs in trypanosomes. Since then, RNA editing has been documented across all domains of life, from viruses to humans. The enzymes that catalyze these reactions are diverse in structure and mechanism, but they share a common feature: they recognize specific RNA substrates and chemically modify them with high precision.
Enzymatic vs. Non-Enzymatic Editing
RNA editing can be broadly classified into two categories based on whether it requires enzymatic catalysis. Enzymatic editing is the dominant form and involves dedicated proteins that recognize and modify RNA. These enzymes include adenosine deaminases acting on RNA (ADARs), apolipoprotein B mRNA editing catalytic polypeptide-like (APOBEC) cytidine deaminases, pentatricopeptide repeat (PPR) proteins, and the multiprotein editosome complex found in trypanosomes.
Non-enzymatic editing is rare and typically refers to spontaneous chemical modifications, such as the deamination of cytosine to uracil that can occur under certain conditions without enzyme catalysis. However, even these reactions are usually accelerated by enzymes in biological systems. For the purposes of this article, the focus is on enzymatic RNA editing, which is the mechanism used by the vast majority of organisms that perform editing. The distinction matters because it affects how we interpret experimental data: if you observe a nucleotide change in an RNA sequence, you must determine whether it arose from an editing enzyme or from a sequencing artifact or spontaneous chemical event.
Key Organisms with Enzymatic RNA Editing
Trypanosomes: U Insertion/Deletion
Trypanosomes, particularly Trypanosoma brucei and Trypanosoma cruzi, are parasitic protozoa that exhibit the most extensive RNA editing known in nature. In their mitochondria, nearly all mRNAs undergo editing, with some transcripts having more than 90% of their final sequence determined by the editing process. The editing involves the insertion and deletion of uridine (U) residues, guided by small non-coding RNAs called guide RNAs (gRNAs).
The classic example is the cytochrome c oxidase subunit III (COX3) mRNA in T. brucei, which requires the insertion of hundreds of uridines and the deletion of dozens more to produce a translatable message. The editing process proceeds in a 3'-to-5' direction along the mRNA, with each gRNA directing editing at a specific block of sequence. Without editing, these mitochondrial transcripts would encode non-functional proteins or no proteins at all, because the unedited sequences contain premature stop codons and shifted reading frames.
Plant Organelles: C-to-U and U-to-C
Plant mitochondria and chloroplasts perform RNA editing extensively, primarily converting cytidine (C) to uridine (U), with rarer U-to-C conversions in some species. In Arabidopsis thaliana, more than 500 C-to-U editing sites exist in the mitochondrial genome and over 30 in the chloroplast genome. These edits often restore conserved amino acid residues or create start and stop codons.
For example, in the mitochondrial nad4 gene of Arabidopsis, editing converts a CGG codon (arginine) to UGG (tryptophan), which is the conserved residue across species. In chloroplasts, the psbE mRNA requires editing to produce a functional cytochrome b559 protein. The enzymes responsible are PPR proteins, which recognize specific cis-elements upstream of the editing site and recruit a cytidine deaminase activity. Unlike trypanosome editing, plant editing does not involve guide RNAs; instead, each PPR protein recognizes a specific RNA sequence motif.
Mammals: A-to-I Editing
In mammals, the predominant form of RNA editing is the deamination of adenosine (A) to inosine (I), catalyzed by ADAR enzymes. Inosine is read as guanosine (G) by the translation machinery, so A-to-I editing effectively produces A-to-G changes in the final protein sequence. This editing occurs primarily in the brain and affects genes involved in neurotransmission.
The best-characterized example is the glutamate receptor subunit GluA2 (encoded by GRIA2). A single editing site in the Q/R site of the mRNA changes a glutamine (Q) codon (CAG) to an arginine (R) codon (CIG, read as CGG). This single amino acid change dramatically alters the calcium permeability of the AMPA receptor. Mice engineered to lack editing at this site develop seizures and die within three weeks of birth, demonstrating the essential nature of this modification.
Other well-studied mammalian editing targets include the serotonin receptor 2C (HTR2C), where editing at multiple sites generates receptor isoforms with different G-protein coupling efficiencies, and the KCNMA1 potassium channel, where editing alters channel inactivation kinetics.
Cephalopods: Extensive Recoding
Cephalopods—octopus, squid, and cuttlefish—have taken A-to-I editing to an extreme. In the squid Doryteuthis pealeii and the octopus Octopus bimaculoides, tens of thousands of editing sites have been identified, many of which recode amino acids in proteins expressed in the nervous system. This is in stark contrast to mammals, where most editing occurs in non-coding regions such as Alu elements and introns.
The recoding in cephalopods is particularly notable because it is used to generate proteomic diversity in the absence of extensive gene duplication. For example, the squid potassium channel Kv1 undergoes editing at multiple sites that alter channel gating properties, allowing the animal to fine-tune neuronal excitability. The evolutionary significance is profound: cephalopods appear to have evolved a nervous system that relies heavily on RNA editing to generate protein diversity, rather than on genomic expansion. This is discussed further in the context of Organism That RNA Editing Enhances Adaptation.
Enzymes Involved in RNA Editing
ADARs (Adenosine Deaminases)
ADARs are a family of enzymes that catalyze the hydrolytic deamination of adenosine to inosine in double-stranded RNA. There are three members in mammals: ADAR1 (encoded by ADAR), ADAR2 (encoded by ADARB1), and ADAR3 (encoded by ADARB2). ADAR1 and ADAR2 are catalytically active, while ADAR3 appears to be catalytically inactive and may act as a regulator.
The enzymes share a common domain architecture: two or three double-stranded RNA binding domains (dsRBDs) at the N-terminus and a deaminase domain at the C-terminus. The deaminase domain contains a zinc-coordinating active site and uses water as the nucleophile to replace the amino group at position 6 of adenosine, converting it to inosine.
ADAR1 exists in two isoforms: a constitutively expressed p110 form and an interferon-inducible p150 form. ADAR2 is constitutively expressed and is responsible for most recoding editing in the brain. The enzymes act on imperfectly base-paired double-stranded RNA structures, with the editing site typically located opposite a mismatched or bulged nucleotide. ADAR1 preferentially edits sites in long, perfectly paired duplexes, such as those formed by Alu repeats, while ADAR2 targets shorter, more structured regions.
The reaction requires no cofactors beyond water and zinc, and the enzymes are active at physiological pH and temperature. In vitro assays typically use 1–10 units of enzyme per microgram of RNA substrate, incubated at 37°C for 1–2 hours in a buffer containing 10 mM Tris-HCl (pH 7.5), 50 mM KCl, and 1 mM MgCl₂.
APOBEC Cytidine Deaminases
The APOBEC family of cytidine deaminases catalyzes the conversion of cytidine to uridine in RNA (and in some cases, deoxycytidine to deoxyuridine in DNA). The founding member, APOBEC1, is responsible for editing apolipoprotein B (APOB) mRNA in the small intestine of mammals.
APOBEC1 edits a single cytidine at position 6666 of the APOB mRNA, converting a glutamine codon (CAA) to a stop codon (UAA). This produces a truncated protein, apoB48, which is essential for chylomicron assembly in the intestine. The full-length protein, apoB100, is produced in the liver where editing does not occur.
APOBEC1 requires a cofactor complex for activity. The minimal complex includes APOBEC1 complementation factor (ACF), which binds to a mooring sequence downstream of the editing site. The mooring sequence is an 11-nucleotide motif (UGAUCAGUAUA) located approximately 20 nucleotides downstream of the edited C. ACF recruits APOBEC1 to the site, and the deamination reaction proceeds.
Other APOBEC family members, such as APOBEC3A and APOBEC3G, primarily act on DNA and are involved in antiviral defense, but they can also edit RNA under certain conditions. The catalytic mechanism involves a zinc ion coordinated by two histidines and a cysteine, with a glutamate acting as a proton shuttle.
PPR Proteins in Plant Editing
Pentatricopeptide repeat (PPR) proteins are a large family of RNA-binding proteins in plants, with over 400 members in Arabidopsis. They are characterized by tandem repeats of a 35-amino-acid motif that forms a helical hairpin structure. Each repeat recognizes one nucleotide of RNA, with amino acid residues at positions 5 and 35 of the repeat determining nucleotide specificity.
In plant RNA editing, PPR proteins act as specificity factors. They bind to cis-elements upstream of editing sites and recruit a cytidine deaminase activity. The deaminase itself is often a separate protein, such as MORF (multiple organellar RNA editing factor) proteins, which interact with PPR proteins to form an editing complex.
The recognition code is degenerate, meaning that multiple PPR proteins can recognize overlapping sequences, and one PPR protein may recognize multiple sites with similar sequences. For example, the PPR protein CLB19 (chloroplast biogenesis 19) is required for editing of rpoA and ndhD transcripts in Arabidopsis chloroplasts. Loss of CLB19 leads to seedling lethality due to impaired chloroplast function.
The mechanism of deamination by PPR-associated factors is less well understood than ADAR or APOBEC, but it is thought to involve a DYW domain (named for its conserved aspartate-tyrosine-tryptophan residues) that contains the catalytic deaminase activity. Some PPR proteins contain the DYW domain themselves, while others recruit separate DYW-containing proteins.
Trypanosome Editosome Complex
The trypanosome editosome is a multiprotein complex that catalyzes U insertion and deletion in mitochondrial mRNAs. The complex is approximately 1.6 MDa in size and contains around 20 proteins, including:
- Endoribonucleases that cleave the mRNA at the editing site
- Terminal uridylyl transferases (TUTases) that add U residues
- Exoribonucleases that remove U residues
- RNA ligases that rejoin the mRNA after editing
The editosome is organized into three functional modules: the RNA recognition module, the catalytic module, and the structural module. The core catalytic proteins include KREPB2 (kinetoplast RNA editing protein B2), which has endoribonuclease activity, and KREL1/KREL2, which are RNA ligases.
The editing reaction is directed by gRNAs, which are small RNAs (40–70 nucleotides) that are complementary to the edited mRNA sequence. The gRNA base-pairs with the mRNA immediately downstream of the editing site, and the unpaired region of the gRNA specifies the number of Us to insert or delete. The editosome then processes the mRNA in a series of steps: cleavage, U addition or removal, and ligation.
Mechanisms of Enzymatic RNA Editing
Deamination Reactions
The most common enzymatic RNA editing reactions are deaminations: the removal of an amino group from a nucleotide base. Two types occur: adenosine deamination (A-to-I) and cytidine deamination (C-to-U).
A-to-I editing is catalyzed by ADARs. The reaction mechanism involves:
- The enzyme binds to double-stranded RNA, with the target adenosine located in a bulged or mismatched region.
- A zinc ion in the active site activates a water molecule.
- The activated water attacks the C6 position of adenosine, forming a tetrahedral intermediate.
- The amino group is released as ammonia, and the intermediate collapses to form inosine.
Inosine is structurally similar to guanosine and base-pairs with cytidine, so the translation machinery reads it as G. This means A-to-I editing effectively produces A-to-G changes in the protein sequence.
C-to-U editing is catalyzed by APOBEC enzymes and PPR-associated deaminases. The mechanism is analogous:
- The enzyme binds to single-stranded RNA at the editing site.
- A zinc-activated water attacks the C4 position of cytidine.
- The amino group is released as ammonia, forming uracil.
C-to-U editing produces a U, which is read as U by the translation machinery. This can change the encoded amino acid or create a stop codon, as in the case of APOB mRNA.
Guide RNA-Directed Editing
Guide RNA-directed editing is mechanistically distinct from deamination. It occurs in trypanosome mitochondria and involves the insertion and deletion of uridines. The process is directed by gRNAs that are transcribed from separate mitochondrial DNA molecules.
The editing reaction proceeds in a 3'-to-5' direction along the mRNA, in a series of steps:
- Anchor duplex formation: The 5' end of the gRNA base-pairs with the mRNA immediately downstream (3') of the region to be edited. This anchor duplex is typically 10–15 base pairs.
- Cleavage: The editosome endoribonuclease cleaves the mRNA at the first unpaired nucleotide, just upstream of the anchor duplex.
- U insertion or deletion: If the gRNA specifies U insertion, a TUTase adds uridines to the 3' end of the 5' cleavage product. The number of Us added is determined by the number of unpaired A or G residues in the gRNA that are opposite the insertion site. If the gRNA specifies U deletion, an exoribonuclease removes uridines from the 3' end of the 5' cleavage product.
- Ligation: The RNA ligase rejoins the two mRNA fragments.
- Translocation: The gRNA/mRNA duplex is unwound, and the process repeats at the next editing site.
This process is highly processive, with a single gRNA directing multiple rounds of editing. The fidelity of editing depends on the precise base-pairing between the gRNA and the mRNA, as well as the accuracy of the editosome's cleavage and ligation activities.
Recognition of Editing Sites
The specificity of RNA editing depends on how enzymes recognize their target sites. Different enzyme families use different strategies:
- ADARs recognize double-stranded RNA structures. The editing site is typically located opposite a mismatch or bulge, which creates a distortion in the helix that the enzyme can detect. The surrounding sequence also contributes to specificity, with a preference for a 5' neighbor that is U or A and a 3' neighbor that is G or U.
- APOBEC1 recognizes a specific sequence context. The mooring sequence (UGAUCAGUAUA) is required for editing of APOB mRNA, and ACF binds to this sequence and recruits APOBEC1. The editing site itself is typically a C that is preceded by a U and followed by a purine.
- PPR proteins recognize specific RNA sequences through their repeat domains. Each PPR repeat binds one nucleotide, and the combination of repeats determines the target sequence. The binding site is typically 20–40 nucleotides upstream of the editing site, and the PPR protein recruits the deaminase to the correct position.
- The editosome recognizes the gRNA/mRNA duplex. The specificity comes from the gRNA sequence, which determines where editing occurs and what changes are made.
Functional Consequences of RNA Editing
Protein Diversity
RNA editing can generate protein diversity by changing codons and thus altering amino acid sequences. This is particularly important in the nervous system, where subtle changes in ion channel or receptor properties can have profound functional consequences.
In mammals, the GluA2 Q/R site editing is a classic example. The unedited form (Q) produces AMPA receptors that are permeable to calcium, while the edited form (R) produces receptors that are impermeable. Since most AMPA receptors in the adult brain contain the edited form, calcium permeability is restricted to specific cell types and developmental stages.
In cephalopods, editing is used much more extensively to generate protein diversity. The squid Kv1 potassium channel has multiple editing sites that alter channel gating, and the combination of edits can produce dozens of different channel variants. This allows the animal to fine-tune neuronal excitability in response to environmental conditions, a strategy that is discussed in Organism That RNA Editing Enhances Adaptation.
Disease Implications
Dysregulation of RNA editing is associated with several human diseases. Reduced A-to-I editing has been observed in many cancers, including glioblastoma, where decreased editing of the GRIA2 Q/R site correlates with increased tumor invasiveness. This is because the unedited, calcium-permeable AMPA receptors promote cell migration and proliferation.
A-to-I editing is also implicated in neurological and psychiatric disorders. Reduced editing of the serotonin receptor 2C (HTR2C) has been reported in suicide victims and in patients with schizophrenia. In amyotrophic lateral sclerosis (ALS), reduced editing of the GRIA2 Q/R site in motor neurons contributes to excitotoxicity and cell death.
Defects in plant RNA editing can cause developmental abnormalities. Mutations in PPR proteins that are required for editing of essential mitochondrial or chloroplast transcripts often result in embryo lethality or severe growth defects. For example, mutations in the PPR gene EMB2654 cause embryo development arrest in Arabidopsis due to loss of editing of the nad1 transcript.
Evolutionary Significance
RNA editing has evolved independently in multiple lineages, suggesting that it provides a selective advantage. In plants, editing is thought to correct mutations that have accumulated in organellar genomes, restoring conserved amino acid sequences. In mammals, editing provides a mechanism for generating protein diversity without requiring genomic changes.
The most striking evolutionary example is in cephalopods, where editing is used to generate extensive proteomic diversity in the nervous system. This has allowed cephalopods to evolve complex behaviors without the large-scale gene duplication events that occurred in vertebrate evolution. The trade-off is that cephalopods have relatively low genomic diversity, making them vulnerable to environmental changes that require rapid adaptation. This trade-off is explored in detail in Organism That RNA Editing Enhances Adaptation.
Methods to Study RNA Editing
High-Throughput Sequencing
RNA sequencing (RNA-seq) is the primary method for identifying RNA editing sites genome-wide. The approach involves:
- Library preparation: Total RNA is isolated, and ribosomal RNA is depleted. The remaining RNA is fragmented and converted to cDNA using reverse transcriptase.
- Sequencing: The cDNA library is sequenced using next-generation sequencing platforms (e.g., Illumina), producing millions of short reads.
- Alignment: The reads are aligned to the reference genome. Reads that contain mismatches at specific positions are candidates for editing sites.
- Filtering: To distinguish true editing sites from sequencing errors or genomic polymorphisms, several filters are applied:
- The mismatch must be present in multiple independent reads.
- The mismatch must be of the expected type (e.g., A-to-G for A-to-I editing).
- The position must not be a known SNP in the reference genome.
- The quality scores of the mismatched bases should be high.
For A-to-I editing, a common approach is to compare RNA-seq data with genomic DNA sequencing data from the same individual. Sites that show A-to-G mismatches in RNA but A in DNA are candidate editing sites.
Targeted Validation
While RNA-seq can identify candidate editing sites, targeted methods are needed for validation and for measuring editing efficiency at specific sites.
RT-PCR and Sanger sequencing: The region of interest is amplified by RT-PCR, and the PCR product is sequenced. The editing efficiency is calculated as the ratio of edited to unedited peaks in the sequencing chromatogram. For example, if the edited base (G) has a peak height that is 50% of the total, the editing efficiency is 50%.
Quantitative PCR (qPCR): For sites where editing creates or destroys a restriction enzyme site, qPCR can be used to measure editing efficiency. The PCR product is digested with the restriction enzyme, and the ratio of digested to undigested product is quantified.
Primer extension assays: A primer is designed to anneal immediately upstream of the editing site. The primer is extended with a DNA polymerase in the presence of a dideoxynucleotide that terminates extension at the editing site. The ratio of terminated to extended products reflects the editing efficiency.
Bioinformatics Prediction
Several computational tools are available for predicting RNA editing sites from sequence data:
- REDIportal: A database of A-to-I editing sites in humans, compiled from multiple RNA-seq datasets.
- DREAM (Disease-Related Editing Analysis Method): A tool for identifying editing sites associated with disease.
- RNAEditor: A tool for detecting editing sites from RNA-seq data, which uses a machine learning approach to distinguish true editing sites from artifacts.
These tools typically require RNA-seq data in BAM format and a reference genome. They apply filters for read quality, mapping quality, and strand specificity, and they report editing sites with associated editing levels.
For biochemical assays, recombinant ADAR or APOBEC enzymes can be expressed in E. coli or insect cells and used for in vitro editing reactions. The RNA substrate is typically a synthetic RNA oligonucleotide or an in vitro transcribed RNA, and the reaction is carried out in a buffer containing 10 mM Tris-HCl (pH 7.5), 50 mM KCl, 1 mM MgCl₂, and 1 mM DTT, at 37°C for 1–2 hours. The editing efficiency is then measured by RT-PCR and sequencing.
Common Pitfalls and Misconceptions
Editing vs. Splicing
A common confusion is between RNA editing and RNA splicing. Splicing removes introns and joins exons, changing the length of the RNA but not the identity of the nucleotides that are retained. Editing changes the identity of individual nucleotides without changing the length of the RNA (except in the case of U insertion/deletion in trypanosomes).
The distinction is important because the two processes are catalyzed by different enzymes and have different regulatory mechanisms. Splicing is carried out by the spliceosome, a large ribonucleoprotein complex, while editing is carried out by deaminases or editosomes. Furthermore, editing can affect splicing by creating or destroying splice sites, but the two processes are mechanistically distinct.
Enzymatic vs. Non-Enzymatic
Not all nucleotide changes in RNA are due to enzymatic editing. Spontaneous deamination of cytosine to uracil can occur at low rates under physiological conditions, and oxidative damage can convert guanosine to 8-oxoguanosine. These non-enzymatic changes are generally rare and are not regulated, whereas enzymatic editing is specific and regulated.
In practice, distinguishing enzymatic from non-enzymatic changes requires experimental evidence. If a nucleotide change is observed consistently across multiple samples and at a specific position, it is likely to be enzymatic. If the change is sporadic or occurs at low frequency, it may be due to damage or sequencing error.
Artifacts in RNA-seq
RNA-seq data can contain artifacts that mimic RNA editing. The most common are:
- Sequencing errors: Base-calling errors can produce mismatches that look like editing sites. These are usually random and occur at low frequency.
- Mapping errors: Reads that map to multiple locations in the genome can produce mismatches that are not true editing sites.
- SNPs: Genomic polymorphisms can be mistaken for editing sites if the reference genome contains the minor allele. This is why it is essential to compare RNA-seq data with genomic DNA data from the same individual.
- RNA modifications: Other RNA modifications, such as m⁶A methylation, can cause base-pairing changes during reverse transcription that produce mismatches in the cDNA.
To avoid these artifacts, it is important to apply stringent filters and to validate candidate sites using independent methods.
Summary and Study Tips
Key Takeaways
- RNA editing is a post-transcriptional process that changes the nucleotide sequence of RNA, and it is catalyzed by enzymes in most organisms.
- The major types of enzymatic editing are A-to-I deamination (by ADARs), C-to-U deamination (by APOBECs and PPR-associated factors), and U insertion/deletion (by the trypanosome editosome).
- RNA editing occurs in trypanosomes, plants, mammals, and cephalopods, with different enzymes and mechanisms in each group.
- Editing has important functional consequences, including altering protein function, generating protein diversity, and contributing to disease when dysregulated.
- RNA editing can be studied using RNA-seq, targeted validation methods, and bioinformatics tools.
Exam Preparation Strategies
- Know the enzymes and their reactions: For each enzyme family (ADAR, APOBEC, PPR, editosome), know the reaction catalyzed, the substrate, and the organism where it is most important.
- Understand the mechanisms: Be able to explain the deamination reaction and the gRNA-directed insertion/deletion mechanism in detail.
- Compare and contrast: Be able to compare RNA editing across organisms, noting the similarities and differences in enzymes and mechanisms.
- Connect to function: Understand how editing affects protein function, using specific examples like GluA2 and APOB.
- Be aware of methods: Know the basic principles of RNA-seq and targeted validation methods for detecting editing sites.
- Avoid common pitfalls: Be clear about the difference between editing and splicing, and be aware of artifacts in RNA-seq data.
Frequently Asked Questions
What organisms have RNA editing that involves enzymes?
Enzymatic RNA editing occurs in trypanosomes (U insertion/deletion in mitochondria), plants (C-to-U and U-to-C in mitochondria and chloroplasts), mammals (A-to-I editing by ADARs), and cephalopods (extensive A-to-I recoding). It has also been reported in viruses, fungi, and other invertebrates, though the extent and mechanisms vary.
Which enzymes are responsible for RNA editing?
The main enzyme families are ADARs (adenosine deaminases acting on RNA), which catalyze A-to-I editing; APOBEC cytidine deaminases, which catalyze C-to-U editing; PPR proteins, which direct C-to-U editing in plant organelles; and the editosome complex in trypanosomes, which catalyzes U insertion/deletion.
How does RNA editing differ from RNA splicing?
Splicing removes introns and joins exons, changing the length of the RNA. Editing changes the identity of individual nucleotides without changing the length (except in trypanosome U insertion/deletion). Splicing is catalyzed by the spliceosome, while editing is catalyzed by deaminases or editosomes.
Is RNA editing always enzyme-dependent?
No. Spontaneous chemical deamination can occur at low rates, but this is rare and unregulated. The vast majority of RNA editing in biological systems is enzyme-dependent, and the enzymes provide specificity and regulation.
What is the role of guide RNAs in RNA editing?
Guide RNAs (gRNAs) are small non-coding RNAs that direct U insertion and deletion in trypanosome mitochondria. They base-pair with the mRNA and specify the number of uridines to insert or delete at each editing site.
How can RNA editing be detected experimentally?
RNA editing can be detected by RNA-seq, which identifies mismatches between RNA and genomic DNA. Candidate sites are validated by RT-PCR and Sanger sequencing, which measures editing efficiency. Bioinformatics tools can predict editing sites from sequence data.
Why is RNA editing important in mammals?
In mammals, A-to-I editing is essential for normal brain function. It alters the properties of glutamate receptors, serotonin receptors, and ion channels, and it is involved in the regulation of gene expression. Dysregulation of editing is associated with cancer, neurological disorders, and psychiatric diseases.
Key Takeaways
- RNA editing is an enzyme-catalyzed process that changes RNA nucleotide sequences post-transcriptionally, distinct from splicing.
- ADARs (A-to-I), APOBECs (C-to-U), PPR proteins (plant C-to-U), and the trypanosome editosome (U insertion/deletion) are the major enzyme systems.
- Trypanosomes, plants, mammals, and cephalopods all use enzymatic editing, but with different mechanisms and extents.
- Editing alters protein function, generates diversity, and is essential for normal physiology; its dysregulation causes disease.
- RNA-seq, RT-PCR, and bioinformatics tools are the standard methods for detecting and quantifying editing sites.
- Distinguishing editing from splicing and from sequencing artifacts is critical for correct interpretation of data.
- Understanding the enzymes, mechanisms, and functional consequences of editing is essential for mastering this topic in molecular biology.