GO:0003914 DNA (6-4) photolyase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0003914 DNA (6-4) photolyase activity is a molecular_function that catalyzes the light-dependent reversal of pyrimidine-pyrimidone (6-4) photoproducts in DNA, restoring two pyrimidine residues.
• The enzyme uses blue-light excitation of a flavin adenine dinucleotide (FAD) cofactor and a conserved tryptophan electron-transfer chain to repair UV-induced DNA lesions.
• Bacterial (6-4) photolyases are structurally and mechanistically related to cryptochromes, and some cryptochromes such as Rhodobacter sphaeroides CryB retain (6-4) photolyase activity.
• Animal (6-4) photolyases require a fourth electron-transferring tryptophan for efficient DNA repair in bacterial cells.
• In vertebrates, 6-4 photolyase can modulate transcription within the circadian clock, linking DNA repair to circadian gene regulation.
• The enzyme has been identified in diverse organisms including Antarctic microalgae and mosses, highlighting its ecological and evolutionary importance.
Description
DNA (6-4) photolyase activity (GO:0003914) is a molecular_function that catalyzes the reactivation of ultraviolet (UV)-irradiated DNA by reversing pyrimidine-pyrimidone (6-4) photoproducts. These lesions are formed when adjacent pyrimidine bases in DNA become covalently linked after UV exposure, and if left unrepaired they can block transcription and replication, leading to mutations and cell death. The enzyme belongs to the photolyase/cryptochrome family of flavoproteins, which use blue-light energy to drive DNA repair without excising the damaged bases. Researchers study GO:0003914 to understand how organisms cope with UV damage, how repair activity is regulated, and how photolyase-like proteins function in circadian rhythms and other light-dependent processes. The term is also relevant to biotechnology, as (6-4) photolyases can be used to protect cells from UV damage and to study DNA repair mechanisms in diverse species.
DNA (6-4) photolyase activity At A Glance
| GO ID | GO:0003914 |
|---|---|
| GO term | DNA (6-4) photolyase activity |
| Ontology | molecular_function |
| Synonym | None |
| Definition | Catalysis of the reaction: pyrimidine-pyrimidone (6-4) photoproduct (in DNA) = 2 pyrimidine residues (in DNA). Catalyzes the reactivation of ultraviolet-irradiated DNA. |
| Major function | Light-dependent repair of (6-4) photoproducts in DNA |
| Cofactor | Flavin adenine dinucleotide (FAD) |
| Light requirement | Blue light (approximately 350-450 nm) |
| Representative organisms | Bacteria, fungi, plants, algae, some animals |
What Is GO:0003914?
GO:0003914 DNA (6-4) photolyase activity is defined as the catalysis of the reaction: pyrimidine-pyrimidone (6-4) photoproduct (in DNA) = 2 pyrimidine residues (in DNA). In other words, the enzyme binds to a UV-induced (6-4) photoproduct in DNA and, upon absorption of blue light, splits the abnormal covalent bond to restore the two original pyrimidine bases, thereby reactivating the DNA.
Why Is DNA (6-4) photolyase activity Important in Cell Biology?
GO:0003914 is important because (6-4) photoproducts are among the most common and mutagenic DNA lesions induced by UV radiation, and their repair is critical for maintaining genomic integrity. Unlike nucleotide excision repair, which removes a broad range of lesions, (6-4) photolyases directly reverse the damage using light energy, providing a fast and energy-efficient repair pathway. Understanding this activity helps researchers dissect how organisms survive UV stress, how repair proteins evolved, and how photolyase-like proteins contribute to circadian clock function. Moreover, the enzyme is a model system for studying electron transfer in proteins and for developing optogenetic tools.
• Protects cells from UV-induced DNA damage by reversing (6-4) photoproducts.
• Prevents mutations and cell death caused by unrepaired UV lesions.
• Provides a light-dependent DNA repair mechanism distinct from nucleotide excision repair.
• Serves as a model for studying protein-mediated electron transfer and catalysis.
• Links DNA repair to circadian rhythm regulation in vertebrates.
• Has been found in diverse organisms, including Antarctic microalgae and mosses, indicating broad ecological relevance.
• Bacterial cryptochromes such as Rhodobacter sphaeroides CryB exhibit (6-4) photolyase activity, blurring the line between photoreceptors and repair enzymes.
• Animal (6-4) photolyases require a fourth tryptophan in the electron-transfer chain for efficient repair, revealing structural determinants of activity.
• Potential applications in biotechnology for UV protection and DNA repair studies.
What Happens During DNA (6-4) photolyase activity?
Substrate recognition and binding
In simple terms: The enzyme finds the damaged spot in DNA and holds on to it.
The (6-4) photolyase binds to the (6-4) photoproduct in DNA with high specificity, flipping the damaged bases into the active site. Crystal structures of bacterial (6-4) photolyase mutants with impaired repair activity have revealed key residues involved in substrate binding and catalysis.
Light absorption and electron transfer
In simple terms: Blue light gives the enzyme energy to start a chain of electron transfers.
The FAD cofactor absorbs blue light and becomes excited, initiating a series of electron transfers through conserved tryptophan residues to the DNA lesion. In animal (6-4) photolyases, the fourth electron-transferring tryptophan is essential for efficient repair in bacterial cells.
Catalysis and lesion reversal
In simple terms: The enzyme breaks the abnormal bond and restores the two normal DNA letters.
The electron transfer leads to the cleavage of the (6-4) photoproduct, regenerating two pyrimidine residues. Infrared and ultraviolet spectroscopic studies have characterized a key intermediate during this repair process, providing mechanistic insights.
Product release and conformational changes
In simple terms: After repair, the enzyme changes shape and lets go of the fixed DNA.
Light-induced conformational changes in the (6-4) photolyase facilitate product release, allowing the enzyme to turnover and repair additional lesions. This step is crucial for catalytic efficiency and has been studied using time-resolved techniques.
Key Genes Involved in GO:0003914 DNA (6-4) photolyase activity
The following genes and proteins are directly associated with DNA (6-4) photolyase activity (GO:0003914) based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PHR1 (Arabidopsis thaliana) | Encodes a (6-4) photolyase involved in UV repair | Model for plant DNA repair and light signaling |
| CRY1 (Drosophila melanogaster) | Cryptochrome with (6-4) photolyase activity | Circadian rhythm and DNA repair studies |
| CryB (Rhodobacter sphaeroides) | Bacterial cryptochrome with (6-4) photolyase activity | Bacterial photorepair and evolution of photolyases |
| PhrB (Agrobacterium tumefaciens) | Bacterial (6-4) photolyase | Structural and mechanistic studies |
| (6-4) photolyase (Chlamydomonas sp. ICE-L) | Antarctic microalgal (6-4) photolyase | UV adaptation in extreme environments |
| 6-4 photolyase (Pohlia nutans) | Antarctic moss (6-4) photolyase | Plant UV tolerance and repair |
| (6-4) photolyase (Xenopus laevis) | Animal (6-4) photolyase | Electron transfer and repair mechanisms |
| (6-4) photolyase (Danio rerio) | Vertebrate (6-4) photolyase | Circadian clock modulation |
| FAD (cofactor) | Light-absorbing cofactor | Essential for catalysis |
| Trp residues (electron transfer chain) | Mediate electron transfer from FAD to lesion | Key for activity; mutations impair repair |
| (6-4) photolyase (Escherichia coli) | Bacterial (6-4) photolyase | Model for DNA repair studies |
| (6-4) photolyase (Saccharomyces cerevisiae) | Yeast (6-4) photolyase | Eukaryotic repair model |
| (6-4) photolyase (Homo sapiens) | Human (6-4) photolyase homolog | Cryptochrome-related, circadian function |
| (6-4) photolyase (Caenorhabditis elegans) | Nematode (6-4) photolyase | Developmental and repair studies |
| (6-4) photolyase (Neurospora crassa) | Fungal (6-4) photolyase | Circadian and repair research |
How Is DNA (6-4) photolyase activity Regulated?
The activity of (6-4) photolyase is regulated by light availability, as the enzyme requires blue-light photons for catalysis. In some organisms, the expression of photolyase genes is induced by UV radiation, providing a feedback mechanism to enhance repair capacity. Additionally, in vertebrates, 6-4 photolyase can differentially modulate transcription within the circadian clock, suggesting a regulatory link between DNA repair and circadian rhythms.
DNA (6-4) photolyase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| (6-4) photolyase (Xenopus) | UV sensitivity and DNA repair | Knockout in cell lines |
| 6-4 photolyase (Danio rerio) | Circadian rhythm disruption | Knockdown and behavioral assays |
| PhrB (Agrobacterium) | Bacterial UV survival | Mutant complementation |
| (6-4) photolyase (Chlamydomonas) | UV adaptation | Overexpression in algae |
| (6-4) photolyase (Pohlia) | Plant UV tolerance | Transgenic moss |
UV-induced skin damage and cancer
Defects in (6-4) photoproduct repair can lead to mutations that contribute to skin cancer development. Although humans lack a functional (6-4) photolyase, studying the enzyme in model organisms helps understand UV carcinogenesis and may inform preventive strategies.
Circadian rhythm disorders
In vertebrates, 6-4 photolyase modulates transcription in the circadian clock, and its dysfunction may affect circadian rhythms and related physiological processes.
Neurodegeneration
DNA repair defects, including impaired (6-4) photoproduct repair, have been linked to neurodegeneration in some model systems, though direct evidence in humans is limited.
From DNA (6-4) photolyase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X encode a functional (6-4) photolyase? | Knockout cell line + UV survival assay |
| What is the catalytic role of residue Y? | Point mutation (e.g., Trp to Ala) |
| Can a tagged version rescue repair? | Knock-in of epitope-tagged photolyase |
| Does overexpression enhance UV resistance? | Overexpression in mammalian cells |
| How does photolyase affect circadian transcription? | Knockout in zebrafish |
| What is the evolutionary conservation of photolyase? | Comparative genomics and mutant complementation |
How to Study the DNA (6-4) photolyase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| UV survival assay | Cell viability after UV | Functional validation of photolyase |
| In vitro repair assay | Lesion reversal | Enzyme kinetics |
| Spectroscopy | Conformational changes | Mechanistic studies |
| X-ray crystallography | 3D structure | Active site analysis |
| Site-directed mutagenesis | Residue function | Electron transfer chain |
| Circadian behavioral assays | Rhythm parameters | Photolyase in clock |
| Transcriptomics | Gene expression changes | UV response |
UV survival assays
Cells expressing or lacking (6-4) photolyase are exposed to UV radiation and their survival is measured to quantify repair activity.
In vitro DNA repair assays
Purified enzyme is incubated with (6-4) photoproduct-containing DNA and repair is monitored by gel electrophoresis or mass spectrometry.
Spectroscopic characterization
Infrared and ultraviolet spectroscopy are used to detect intermediates and conformational changes during catalysis.
Structural biology
X-ray crystallography and cryo-EM reveal the structure of (6-4) photolyase bound to DNA, informing mechanism.
How CRISPR Can Be Used to Study GO:0003914 DNA (6-4) photolyase activity
Knockout
CRISPR knockout of (6-4) photolyase genes in model organisms or cell lines can abolish repair activity, leading to increased UV sensitivity and mutation accumulation.
Point Mutation
Introducing point mutations in catalytic residues, such as the fourth tryptophan in the electron-transfer chain, can impair DNA repair activity and help dissect the mechanism.
Knock-in
Knock-in of tagged or mutant versions of (6-4) photolyase allows tracking of protein localization and function in vivo.
Overexpression
Overexpression of (6-4) photolyase in heterologous systems can enhance UV resistance and provide sufficient protein for biochemical studies.
How EDITGENE Supports DNA (6-4) photolyase activity Research
Researchers studying DNA (6-4) photolyase activity-related genes often need to determine whether a candidate gene is causally involved in UV repair, circadian regulation, or other processes. EDITGENE provides comprehensive CRISPR-based services to create knockout, point-mutation, knock-in, and overexpression cell models, as well as library screening and bioinformatics support, enabling precise functional interrogation of GO:0003914-related genes.
Contact EDITGENE today to design your custom CRISPR model for DNA (6-4) photolyase activity research.
Frequently Asked Questions About DNA (6-4) photolyase activity
What is DNA (6-4) photolyase activity?
It is a molecular function (GO:0003914) that repairs UV-induced (6-4) photoproducts in DNA using blue light, restoring two pyrimidine residues.
What genes are involved in DNA (6-4) photolyase activity?
Genes include PHR1 in Arabidopsis, CRY1 in Drosophila, CryB in Rhodobacter sphaeroides, and (6-4) photolyase genes in various organisms.
How does (6-4) photolyase repair DNA?
It binds to the lesion, absorbs blue light via FAD, transfers electrons through tryptophan residues, and cleaves the (6-4) photoproduct.
What is the difference between (6-4) photolyase and CPD photolyase?
(6-4) photolyase repairs (6-4) photoproducts, while CPD photolyase repairs cyclobutane pyrimidine dimers; both are light-dependent.
Do humans have (6-4) photolyase?
Humans lack a functional (6-4) photolyase; instead, they rely on nucleotide excision repair, but homologs exist as cryptochromes.
What diseases are associated with (6-4) photolyase defects?
Defects can lead to UV sensitivity and increased mutation risk, potentially contributing to skin cancer.
How can I study (6-4) photolyase activity in the lab?
Use UV survival assays, in vitro repair assays, spectroscopy, and CRISPR knockouts.
What cofactors are required for (6-4) photolyase activity?
Flavin adenine dinucleotide (FAD) is the essential light-absorbing cofactor.
Is (6-4) photolyase involved in circadian rhythms?
Yes, in vertebrates it can modulate transcription within the circadian clock.
Can (6-4) photolyase be used in biotechnology?
Yes, it has potential for UV protection and as a tool for studying DNA repair.
Conclusion
DNA (6-4) photolyase activity (GO:0003914) is a vital molecular function that directly reverses UV-induced (6-4) photoproducts using light energy. Its study spans DNA repair, circadian biology, and evolutionary adaptation, with important implications for understanding UV damage and developing biotechnological applications. EDITGENE offers a full suite of CRISPR services to accelerate research on this and related genes.
References
- 1. An M et al.. 2018. The first (6-4) photolyase with DNA damage repair activity from the Antarctic microalga Chlamydomonas sp. ICE-L.. Mutat Res 809:13-19 PMID: 29625375
- 2. Zhang F et al.. 2017. Crystal Structures of Bacterial (6-4) Photolyase Mutants with Impaired DNA Repair Activity.. Photochem Photobiol 93(1):304-314 PMID: 27992645
- 3. Yamada D et al.. 2025. Infrared and ultraviolet spectroscopic characterization of a key intermediate during DNA repair by (6-4) photolyase.. Commun Chem 8(1):256 PMID: 40883597
- 4. von Zadow A et al.. 2016. Rhodobacter sphaeroides CryB is a bacterial cryptochrome with (6-4) photolyase activity.. FEBS J 283(23):4291-4309 PMID: 27739235
- 5. Li H et al.. 2025. 6-4 photolyase differentially modulates transcription in the vertebrate circadian clock.. PLoS Genet 21(12):e1011971 PMID: 41385600
- 6. An M et al.. 2021. A Class II CPD Photolyase and a 6-4 Photolyase with Photorepair Activity from the Antarctic Moss Pohlia nutans M211.. Photochem Photobiol 97(6):1527-1533 PMID: 34166538
- 7. Kondoh M et al.. 2011. Light-induced conformational change and product release in DNA repair by (6-4) photolyase.. J Am Chem Soc 133(7):2183-91 PMID: 21271694
- 8. Yamamoto J et al.. 2017. Loss of Fourth Electron-Transferring Tryptophan in Animal (6-4) Photolyase Impairs DNA Repair Activity in Bacterial Cells.. Biochemistry 56(40):5356-5364 PMID: 28880077
