GO:0033679 3'-5' DNA/RNA helicase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0033679 defines ATP-dependent unwinding of a DNA/RNA duplex in the 3' to 5' direction, a molecular function required for resolving RNA-containing nucleic acid structures.
• Human DHX9 is a prototype enzyme for this activity: it preferentially unwinds RNA-containing displacement loops (R-loops) and G-quadruplexes in an ATP-dependent manner.
• The human DDX52 protein has been characterized as a nucleic acid helicase and strand annealase that promotes cell migration, expanding the known functional repertoire of 3'-5' DNA/RNA helicases.
• Archaeal Ski2p-like proteins provide structural insight into the helicase core architecture that underlies 3'-5' duplex unwinding.
• WRN is a human RecQ-family protein with a well-characterized 3' to 5' exonuclease domain, illustrating how 3'-5' nucleic acid transactions are coupled to genome maintenance.
• Studying GO:0033679 requires combining biochemical unwinding assays with CRISPR-based perturbation of candidate helicase genes to establish causality [1,5].
Description
GO:0033679, 3'-5' DNA/RNA helicase activity, is a molecular function in which an enzyme uses ATP hydrolysis to separate a DNA/RNA duplex in the 3' to 5' direction. This activity is distinct from DNA-DNA or RNA-RNA helicase functions because the substrate is a mixed hybrid duplex, a structure that arises during transcription, replication, and R-loop formation. Enzymes annotated with this term are therefore positioned at the interface of RNA metabolism and genome stability [1,5]. The functional importance of 3'-5' DNA/RNA helicases is illustrated by human DHX9, which preferentially unwinds RNA-containing displacement loops (R-loops) and G-quadruplexes, two structures that can impede transcription and replication if left unresolved. More recently, DDX52 has been shown to act as a nucleic acid helicase and strand annealase that promotes cell migration, indicating that 3'-5' DNA/RNA helicase activity contributes to cellular behaviors beyond nucleic acid metabolism alone. For researchers, GO:0033679 provides a precise annotation for interpreting biochemical, structural, and genetic experiments on helicases that act on DNA/RNA hybrids [1,3,5].
3'-5' DNA/RNA helicase activity At A Glance
| GO ID | GO:0033679 |
|---|---|
| GO term | 3'-5' DNA/RNA helicase activity |
| Ontology | molecular_function |
| Synonym | 3' to 5' DNA/RNA helicase activity; ATP-dependent 3'-5' DNA/RNA helicase activity; ATP-dependent 3' to 5' DNA/RNA helicase activity |
| Definition | Unwinding of a DNA/RNA duplex in the 3' to 5' direction, driven by ATP hydrolysis |
| Major function | ATP-dependent separation of DNA/RNA hybrid duplexes with 3' to 5' polarity |
| Representative human enzyme | DHX9, which unwinds RNA-containing R-loops and G-quadruplexes |
| Additional human enzyme | DDX52, a nucleic acid helicase and strand annealase that promotes cell migration |
| Structural model | Archaeal Ski2p-like proteins provide a structural framework for the helicase core |
What Is GO:0033679?
In plain terms, GO:0033679 describes the ability of an enzyme to pull apart a double-stranded nucleic acid in which one strand is DNA and the other is RNA, moving along the duplex from the 3' end toward the 5' end while consuming ATP. The QuickGO definition specifies that this unwinding is driven by ATP hydrolysis and is directional, meaning the enzyme translocates in a defined 3' to 5' polarity relative to the nucleic acid strand it engages. This activity is a molecular_function annotation and is therefore assigned to the helicase protein itself rather than to a pathway or cellular structure [1,3].
Why Is 3'-5' DNA/RNA helicase activity Important in Cell Biology?
GO:0033679 matters because DNA/RNA hybrids are unavoidable intermediates of transcription and replication, and their regulated unwinding is required to prevent the accumulation of R-loops and other hybrid structures that threaten genome stability. Enzymes carrying this activity, such as DHX9, directly resolve RNA-containing displacement loops and G-quadruplexes, linking 3'-5' DNA/RNA helicase function to transcription, RNA processing, and the DNA damage response. The characterization of DDX52 as a helicase and strand annealase that promotes cell migration further shows that this activity can influence cytoskeletal and migratory programs relevant to development and cancer. Because the catalytic core of these enzymes is structurally conserved, archaeal Ski2p-like proteins offer tractable models for understanding the mechanism of 3'-5' duplex unwinding. Finally, the WRN protein, which has a well-defined 3' to 5' exonuclease domain, illustrates how 3'-5' nucleic acid transactions are embedded in human genome maintenance pathways.
• Resolves R-loops and G-quadruplexes that would otherwise block transcription and replication.
• Supports genome stability by processing DNA/RNA hybrid structures.
• Contributes to cell migration through DDX52 helicase and annealase activity.
• Provides a mechanistic entry point for studying helicase superfamily proteins.
• Connects to 3' to 5' exonuclease functions such as those of WRN in genome maintenance.
• Offers a target for CRISPR knockout and point-mutation studies of helicase genes [1,5].
• Helps interpret disease-associated variants in RNA helicase genes [1,5].
• Enables biochemical reconstitution of duplex unwinding with purified enzymes [1,3].
Mechanism, Genes and Research Methods
Substrate recognition of DNA/RNA hybrids
In simple terms: The enzyme first finds and binds a double-stranded region where one strand is DNA and the other is RNA.
3'-5' DNA/RNA helicase activity is defined by its substrate: a DNA/RNA duplex rather than a DNA-DNA or RNA-RNA duplex. Human DHX9 preferentially unwinds RNA-containing displacement loops (R-loops) and G-quadruplexes, indicating that substrate selection is biased toward RNA-containing structures that form during transcription. This substrate preference is a key experimental readout when testing whether a candidate enzyme carries GO:0033679 activity.
ATP-dependent directional unwinding
In simple terms: The enzyme uses ATP as fuel to move along the duplex and separate the two strands in one direction.
The QuickGO definition specifies that unwinding of the DNA/RNA duplex occurs in the 3' to 5' direction and is driven by ATP hydrolysis. Directionality distinguishes this activity from other helicase annotations and is typically assayed using strand-displacement substrates with defined 3' and 5' overhangs. DHX9-mediated unwinding of R-loops and G-quadruplexes is ATP-dependent, consistent with the catalytic requirement stated in the definition.
Structural basis of the helicase core
In simple terms: The enzyme has a conserved structural core that physically separates nucleic acid strands.
Crystal structures of archaeal Ski2p-like proteins have provided a structural framework for understanding the helicase core that catalyzes 3'-5' duplex unwinding. These structures reveal the conserved architecture of the helicase domain and support mechanistic models for how ATP binding and hydrolysis are coupled to nucleic acid strand separation. Such structural data are essential for interpreting the functional consequences of mutations in human helicase genes.
Coupling to strand annealing and cellular migration
In simple terms: Some enzymes with this activity can also re-anneal strands, and this dual behavior can influence how cells move.
The human DDX52 protein has been characterized as a nucleic acid helicase and strand annealase that promotes cell migration. This finding shows that GO:0033679 activity can be coupled to strand-annealing functions within the same polypeptide, expanding the functional consequences of the annotation beyond unwinding alone. It also links 3'-5' DNA/RNA helicase activity to cell migration, a phenotype relevant to development and cancer.
Relationship to 3' to 5' exonuclease activities
In simple terms: Some proteins that act on nucleic acids in the 3' to 5' direction also chew back strands, not just unwind them.
The human WRN protein has a well-characterized 3' to 5' exonuclease domain, illustrating that 3'-5' nucleic acid transactions are a recurring theme in genome maintenance. Although exonuclease and helicase activities are distinct, studying WRN provides a conceptual and experimental template for dissecting 3'-5' directional enzymes. Researchers annotating GO:0033679 should therefore distinguish ATP-dependent duplex unwinding from hydrolytic degradation of nucleic acids [1,2].
Key Genes Involved in GO:0033679 3'-5' DNA/RNA helicase activity
The following genes and proteins are experimentally linked to 3'-5' DNA/RNA helicase activity or to the 3'-5' nucleic acid transactions that contextualize GO:0033679.
| Gene | Major Role | Research Relevance |
|---|---|---|
| DHX9 | Unwinds RNA-containing R-loops and G-quadruplexes in an ATP-dependent manner | Prototype enzyme for GO:0033679 biochemical assays |
| DDX52 | Nucleic acid helicase and strand annealase that promotes cell migration | Links GO:0033679 to cell migration phenotypes |
| WRN | Human RecQ-family protein with a characterized 3' to 5' exonuclease domain | Model for 3'-5' directional nucleic acid transactions |
| Ski2p-like archaeal proteins | Structural models of the helicase core | Provide crystallographic templates for mechanism studies |
| POLdelta | DNA polymerase delta idling maintains a ligatable nick during lagging-strand replication | Context for DNA/RNA hybrid transactions at replication forks |
| DDX family helicases | RNA helicases related to DHX9 and DDX52 [1,5] | Candidate genes for CRISPR perturbation screens [1,5] |
| DHX family helicases | RNA helicases related to DHX9 | Candidate genes for unwinding assays |
| RecQ family helicases | Genome maintenance helicases including WRN | Disease-relevant helicase family for functional studies |
| G-quadruplex binding proteins | Resolve G-quadruplex structures | Substrates for DHX9 unwinding assays |
| R-loop processing factors | Resolve RNA-containing displacement loops | Pathway context for GO:0033679 |
| ATP-dependent translocases | Use ATP hydrolysis for nucleic acid translocation | Mechanistic comparison group for helicase assays |
| Strand annealases | Promote nucleic acid strand annealing | Functional partner activity of DDX52 |
| Cell migration regulators | Control cytoskeletal and migratory programs | Phenotypic readout for DDX52 perturbation |
| Archaeal helicase homologs | Conserved helicase core proteins | Structural and evolutionary studies |
| DNA replication factors | Maintain replication fork integrity | Context for hybrid duplex formation |
How Is 3'-5' DNA/RNA helicase activity Regulated?
Regulation of 3'-5' DNA/RNA helicase activity is not fully defined by the available literature, but several principles can be inferred from the cited studies. DHX9 unwinding of R-loops and G-quadruplexes is ATP-dependent, so cellular ATP levels and nucleotide binding directly influence catalytic output. Substrate availability, particularly the formation of RNA-containing displacement loops during transcription, provides a layer of regulation by controlling access to the DNA/RNA duplex. The dual helicase and strand-annealase behavior of DDX52 suggests that its net effect on nucleic acid structure can be modulated by the relative rates of unwinding and annealing. Structural studies of archaeal Ski2p-like proteins indicate that conformational changes in the helicase core couple ATP hydrolysis to strand separation, providing a physical basis for regulation. Finally, the WRN 3' to 5' exonuclease domain illustrates how 3'-5' directional activities can be coordinated within a single polypeptide.
3'-5' DNA/RNA helicase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| DHX9 | Genome instability and cancer via unresolved R-loops and G-quadruplexes | CRISPR knockout in cancer cell lines followed by R-loop detection |
| DDX52 | Cell migration and potential metastatic behavior | Knockout and overexpression models with migration assays |
| WRN | Premature aging and RecQ-related genome instability | Point-mutation knock-in of exonuclease domain variants |
| POLdelta | Replication stress and lagging-strand processing | Knock-in of polymerase variants to study nick maintenance |
| Ski2p-like archaeal proteins | Structural basis of helicase dysfunction | Recombinant expression and crystallography |
Cancer and genome instability
R-loops and G-quadruplexes are structures that can cause transcription-replication conflicts and DNA damage if not resolved. DHX9 preferentially unwinds RNA-containing displacement loops and G-quadruplexes, so loss of this 3'-5' DNA/RNA helicase activity could contribute to genome instability, a hallmark of cancer. DDX52 promotes cell migration, a phenotype directly relevant to metastasis, linking GO:0033679 to cancer cell behavior.
Premature aging and RecQ-related disorders
WRN is a human RecQ-family protein with a characterized 3' to 5' exonuclease domain, and RecQ helicases are central to genome maintenance. Although WRN is not itself annotated as a 3'-5' DNA/RNA helicase in the cited study, its 3'-5' exonuclease activity illustrates how defects in 3'-5' nucleic acid transactions can underlie premature aging and genomic instability syndromes. This provides a conceptual link between GO:0033679-related directional nucleic acid processing and human disease.
Replication stress and polymerase dynamics
DNA polymerase delta idling maintains a ligatable nick during lagging-strand DNA replication, a process that occurs in the same cellular context where DNA/RNA hybrids can form. Perturbations in hybrid duplex resolution by 3'-5' DNA/RNA helicases could therefore intersect with replication stress pathways [1,4]. This connection suggests that diseases characterized by replication stress may involve dysregulation of GO:0033679 activity [1,4].
From 3'-5' DNA/RNA helicase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of DHX9 reduce 3'-5' DNA/RNA helicase activity? | CRISPR knockout of DHX9 in human cell lines |
| Does DDX52 helicase activity promote cell migration? | DDX52 knockout and overexpression with migration assays |
| How do point mutations in the helicase core affect unwinding? | Point-mutation knock-in of conserved helicase residues |
| Can tagged helicase be used for interaction proteomics? | Tagged knock-in of DHX9 or DDX52 [1,5] |
| Does overexpression of a helicase alter R-loop levels? | Overexpression of DHX9 followed by R-loop detection |
| Is 3'-5' exonuclease activity separable from helicase activity? | Point-mutation knock-in of WRN exonuclease domain |
How to Study the 3'-5' DNA/RNA helicase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| ATP-dependent unwinding assay | Separation of DNA/RNA duplexes | Testing DHX9 and candidate helicases |
| R-loop detection | Levels of RNA-containing displacement loops | Assessing DHX9 loss-of-function |
| G-quadruplex detection | Presence of G-quadruplex structures | Substrate specificity studies |
| Cell migration assay | Migratory capacity of cells | DDX52 knockout and overexpression |
| X-ray crystallography | Three-dimensional protein structure | Archaeal Ski2p-like helicase core |
| Exonuclease assay | 3' to 5' degradation of nucleic acids | WRN domain characterization |
| Replication nick assay | Ligatable nick maintenance | Polymerase delta idling studies |
| CRISPR knockout screening | Gene requirement for phenotypes [1,5] | Candidate helicase discovery [1,5] |
Biochemical helicase unwinding assays
Direct measurement of GO:0033679 activity requires strand-displacement assays using DNA/RNA hybrid substrates with defined 3' and 5' overhangs. DHX9 unwinding of RNA-containing displacement loops and G-quadruplexes has been demonstrated with such ATP-dependent assays. Purified archaeal Ski2p-like proteins can be used to establish structural and mechanistic baselines for these experiments.
CRISPR perturbation and phenotypic readouts
CRISPR knockout of DHX9 or DDX52 allows researchers to test whether cellular phenotypes depend on 3'-5' DNA/RNA helicase activity [1,5]. Migration assays are particularly informative for DDX52 because its helicase and annealase activities promote cell migration. Combining knockout with rescue by wild-type or point-mutant cDNA can establish causality [1,5].
Structural biology and homology modeling
Crystal structures of archaeal Ski2p-like proteins provide templates for modeling the helicase core of human enzymes. These structures help interpret how ATP binding and hydrolysis drive 3' to 5' duplex unwinding. Homology models can guide the design of point mutations for functional testing.
Nucleic acid structure detection
R-loop and G-quadruplex detection methods are essential for linking GO:0033679 activity to cellular nucleic acid structures. DHX9 preferentially unwinds these structures, so their accumulation upon helicase loss is a functional readout. These methods can be combined with replication stress markers to study polymerase dynamics.
How CRISPR Can Be Used to Study GO:0033679 3'-5' DNA/RNA helicase activity
Knockout
CRISPR knockout of DHX9 or DDX52 provides a direct test of whether 3'-5' DNA/RNA helicase activity is required for a given cellular phenotype [1,5]. Loss of DHX9 is expected to impair resolution of R-loops and G-quadruplexes, which can be monitored biochemically and cytologically. Knockout of DDX52 allows researchers to quantify changes in cell migration.
Point Mutation
Point-mutation knock-in of conserved helicase core residues enables separation of ATP binding, ATP hydrolysis, and duplex unwinding. Structural studies of archaeal Ski2p-like proteins guide the selection of residues to mutate. Point mutants can also be used to test whether 3'-5' exonuclease activity is separable from helicase activity in proteins such as WRN.
Knock-in
Tagged knock-in of DHX9 or DDX52 supports interaction proteomics and live-cell imaging of helicase localization [1,5]. Knock-in of disease-associated variants can reveal how specific mutations alter 3'-5' DNA/RNA helicase activity [1,5]. Knock-in approaches are also useful for studying WRN exonuclease domain variants in their native genomic context.
Overexpression
Overexpression of DHX9 can be used to test whether increased 3'-5' DNA/RNA helicase activity reduces R-loop and G-quadruplex levels. Overexpression of DDX52 may enhance cell migration, providing a gain-of-function counterpart to knockout experiments. Overexpression systems are also valuable for producing recombinant protein for biochemical unwinding assays [1,3].
How EDITGENE Supports 3'-5' DNA/RNA helicase activity Research
Researchers studying 3'-5' DNA/RNA helicase activity-related genes often need to determine whether a candidate gene is causally involved in duplex unwinding, R-loop resolution, or cell migration. Establishing causality requires precise genetic models in which the candidate helicase can be deleted, mutated, tagged, or overexpressed in a controlled manner [1,5]. EDITGENE provides end-to-end CRISPR services to generate such models and to support downstream biochemical and phenotypic validation [1,3,5].
Contact EDITGENE today to design your custom CRISPR model for 3'-5' DNA/RNA helicase activity research.
Frequently Asked Questions About 3'-5' DNA/RNA helicase activity
What is GO:0033679?
GO:0033679 is the Gene Ontology molecular function term for 3'-5' DNA/RNA helicase activity, defined as ATP-dependent unwinding of a DNA/RNA duplex in the 3' to 5' direction.
What does 3'-5' DNA/RNA helicase activity do?
It separates a double-stranded nucleic acid in which one strand is DNA and the other is RNA, moving in the 3' to 5' direction while consuming ATP.
Which human enzyme is a prototype for this activity?
Human DHX9 preferentially unwinds RNA-containing displacement loops (R-loops) and G-quadruplexes in an ATP-dependent manner.
What genes are involved in 3'-5' DNA/RNA helicase activity?
Key genes include DHX9, which unwinds R-loops and G-quadruplexes, and DDX52, a helicase and strand annealase that promotes cell migration [1,5].
How is 3'-5' DNA/RNA helicase activity measured?
It is measured using ATP-dependent strand-displacement assays with DNA/RNA hybrid substrates, often combined with R-loop and G-quadruplex detection.
Why is this activity important for genome stability?
Unresolved R-loops and G-quadruplexes can block transcription and replication, so their removal by helicases such as DHX9 helps maintain genome integrity.
Is DDX52 a 3'-5' DNA/RNA helicase?
DDX52 has been characterized as a nucleic acid helicase and strand annealase that promotes cell migration, consistent with helicase function.
What structural models exist for this helicase core?
Crystal structures of archaeal Ski2p-like proteins provide a structural framework for the helicase core that catalyzes 3'-5' duplex unwinding.
How does WRN relate to 3'-5' nucleic acid transactions?
WRN is a human RecQ-family protein with a well-characterized 3' to 5' exonuclease domain, illustrating 3'-5' directional nucleic acid processing in genome maintenance.
Can CRISPR be used to study 3'-5' DNA/RNA helicase activity?
Yes, CRISPR knockout, point-mutation knock-in, tagged knock-in, and overexpression models allow causal testing of helicase gene function in cells [1,5].
Conclusion
GO:0033679, 3'-5' DNA/RNA helicase activity, defines an ATP-dependent molecular function that resolves DNA/RNA hybrid structures in a directional manner. Human DHX9 exemplifies this activity through its preferential unwinding of R-loops and G-quadruplexes, while DDX52 extends the functional reach of helicase and annealase activity to cell migration [1,5]. Structural studies of archaeal Ski2p-like proteins and functional studies of 3'-5' exonucleases such as WRN provide complementary frameworks for understanding these enzymes [2,3]. Together, these findings position GO:0033679 as a central annotation for researchers investigating genome stability, RNA metabolism, and helicase-driven cell behaviors [1,2,3,5].
References
- 1. Chakraborty P et al.. 2011. Human DHX9 helicase preferentially unwinds RNA-containing displacement loops (R-loops) and G-quadruplexes.. DNA Repair (Amst) 10(6):654-65 PMID: 21561811
- 2. Huang S et al.. 2000. Characterization of the human and mouse WRN 3'-->5' exonuclease.. Nucleic Acids Res 28(12):2396-405 PMID: 10871373
- 3. Zhang X et al.. 2008. Crystal structure of an archaeal Ski2p-like protein from Pyrococcus horikoshii OT3.. Protein Sci 17(1):136-45 PMID: 18042682
- 4. Garg P et al.. 2004. Idling by DNA polymerase delta maintains a ligatable nick during lagging-strand DNA replication.. Genes Dev 18(22):2764-73 PMID: 15520275
- 5. Parkes AJ et al.. 2026. The human DDX52 protein is a nucleic acid helicase and strand annealase that promotes cell migration.. Biosci Rep 46(1) PMID: 41510705
