ATP-dependent DNA helicase UvsW (also known as Dar) is a 502-amino-acid superfamily 2 (SF2) 3'-5' branched-DNA helicase and strand-annealing motor of bacteriophage T4. Combining two RecA-like ATPase domains with a basic N-terminal branched-substrate recognition domain, UvsW couples ATP hydrolysis to 3'-5' translocation on single-stranded DNA, unwinding of RNA-DNA hybrids (R-loops) and branched DNA duplexes, and complementary strand annealing. In vivo, UvsW represses origin-dependent replication initiation during late infection by unwinding origin R-loops, catalyzes Holliday junction branch migration during homologous recombination, and drives regression of stalled replication forks to promote template-switching DNA repair.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | MODIFY | Summary: UvsW binds ATP at its conserved superfamily 2 RecA-like motor core. Reason: Nucleotide binding (GO:0000166) is overly general; ATP binding (GO:0005524) is already present and specifically captures the physiological nucleotide ligand of UvsW. Proposed replacements: ATP binding Supporting Evidence: PMID:9233823 In support of this model, a partially purified GST/UvsW fusion protein, but not a GST/UvsW-K141R fusion, displays ssDNA-dependent ATPase activity and is able to unwind a branched DNA substrate. |
| GO:0003677 DNA binding | IEA GO_REF:0000120 | ACCEPT | Summary: UvsW binds single-stranded DNA, stalled replication forks, and Holliday junctions via its N-terminal substrate-binding domain and RecA-like motor cleft. Reason: Direct binding to ssDNA and branched DNA junctions is essential for UvsW ATPase activation, branch migration, and strand annealing. Supporting Evidence: PMID:17092935 UvsW is a 3' to 5' helicase that unwinds a wide variety of substrates, including those resembling stalled replication forks and recombination intermediates. UvsW also contains a potent single-strand DNA annealing activity that is enhanced by ATP hydrolysis but does not require it. |
| GO:0004386 helicase activity | IEA GO_REF:0000043 | MODIFY | Summary: UvsW is an ATP-dependent 3'-5' helicase that unwinds branched DNA duplexes and RNA-DNA hybrids. Reason: Helicase activity (GO:0004386) is too general when the specific child term 3'-5' DNA helicase activity (GO:0043138) is already annotated and experimentally verified. Proposed replacements: 3'-5' DNA helicase activity Supporting Evidence: PMID:17092935 UvsW is a 3' to 5' helicase that unwinds a wide variety of substrates, including those resembling stalled replication forks and recombination intermediates. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | ACCEPT | Summary: UvsW binds ATP at its Walker A/B motifs (including Lys141) to power DNA unwinding and branch migration. Reason: ATP binding is required for UvsW ATPase and helicase activities, as shown by inactivation of the Walker A K141R mutant (PMID:9233823). Supporting Evidence: PMID:9233823 In support of this model, a partially purified GST/UvsW fusion protein, but not a GST/UvsW-K141R fusion, displays ssDNA-dependent ATPase activity and is able to unwind a branched DNA substrate. |
| GO:0016787 hydrolase activity | IEA GO_REF:0000120 | MODIFY | Summary: UvsW hydrolyzes ATP to drive 3'-5' branched-DNA unwinding and Holliday junction branch migration. Reason: Hydrolase activity (GO:0016787) is overly broad; the specific descendant terms 3'-5' DNA helicase activity (GO:0043138) and ATP hydrolysis activity (GO:0016887) are already present in the review. Proposed replacements: 3'-5' DNA helicase activity ATP hydrolysis activity Supporting Evidence: PMID:17092935 UvsW is a 3' to 5' helicase that unwinds a wide variety of substrates, including those resembling stalled replication forks and recombination intermediates. UvsW also contains a potent single-strand DNA annealing activity that is enhanced by ATP hydrolysis but does not require it. |
| GO:0016853 isomerase activity | IEA GO_REF:0000043 | MODIFY | Summary: UvsW is an ATP-dependent 3'-5' DNA/RNA helicase classified under EC 5.6.2.4; refine broad isomerase mapping to 3'-5' DNA helicase activity. Reason: DNA helicases (EC 5.6.2.-) were reclassified by IUBMB into EC class 5 (isomerases, UniProt keyword KW-0413), which generates the broad GO:0016853 isomerase activity IEA mapping. Because UvsW specifically catalyzes ATP-dependent 3'-5' DNA/RNA duplex unwinding and Holliday junction branch migration (EC 5.6.2.4), this broad mapping should be refined to GO:0043138 (3'-5' DNA helicase activity). Proposed replacements: 3'-5' DNA helicase activity Supporting Evidence: file:BPT4/uvsW/uvsW-uniprot.txt EC=5.6.2.4 PMID:17823128 Using a novel Holliday junction-containing substrate, we also demonstrate that UvsW promotes the branch migration of Holliday junctions efficiently through more than 1000 bp of DNA. |
| GO:0043138 3'-5' DNA helicase activity | IEA GO_REF:0000003 | ACCEPT | Summary: UvsW unwinds branched DNA substrates, Holliday junctions, and R-loops with 3' to 5' polarity. Reason: 3'-5' DNA helicase activity (GO:0043138) is the core catalytic activity of UvsW, directly demonstrated in PMID:17092935. Supporting Evidence: PMID:17092935 UvsW is a 3' to 5' helicase that unwinds a wide variety of substrates, including those resembling stalled replication forks and recombination intermediates. file:BPT4/uvsW/uvsW-deep-research-falcon.md **Primary function:** UvsW is an ATP-dependent, SF2, 3′→5′ **branch-specific helicase/rewinding motor** that remodels R-loops, replication forks, Holliday junctions, and recombination intermediates. |
| GO:0016887 ATP hydrolysis activity | EXP PMID:17092935 The T4 phage UvsW protein contains both DNA unwinding and st... | ACCEPT | Summary: Purified UvsW catalyzes DNA-dependent ATP hydrolysis that powers 3'-5' branched-DNA unwinding and enhances complementary single-strand DNA annealing. Reason: PMID:17092935 directly demonstrates DNA-dependent ATP hydrolysis by UvsW and its role in driving helicase unwinding and stimulating strand annealing. Supporting Evidence: PMID:17092935 UvsW is a 3' to 5' helicase that unwinds a wide variety of substrates, including those resembling stalled replication forks and recombination intermediates. UvsW also contains a potent single-strand DNA annealing activity that is enhanced by ATP hydrolysis but does not require it. |
| GO:0016887 ATP hydrolysis activity | EXP PMID:9233823 Bacteriophage T4 UvsW protein is a helicase involved in reco... | ACCEPT | Summary: Purified wild-type GST-UvsW, but not the Walker A active-site mutant GST-UvsW-K141R, exhibits ssDNA-dependent ATPase activity coupled to branched DNA unwinding. Reason: PMID:9233823 provides direct biochemical and mutational proof of UvsW ssDNA-dependent ATP hydrolysis activity. Supporting Evidence: PMID:9233823 In support of this model, a partially purified GST/UvsW fusion protein, but not a GST/UvsW-K141R fusion, displays ssDNA-dependent ATPase activity and is able to unwind a branched DNA substrate. |
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Download this section (compressed HTML)Q: How does the basic N-terminal domain of UvsW coordinate simultaneous duplex unwinding and nascent-strand annealing to drive unidirectional regression of stalled replication forks?
Q: What determines whether a Holliday junction or D-loop intermediate in T4-infected cells is resolved by endonuclease VII (gp49) cleavage vs migrated to completion by UvsW?
Experiment: Determine cryo-EM structures of full-length UvsW bound to a four-way Holliday junction and a three-way replication fork in the presence of ADP-AlF4.
Hypothesis: The N-terminal basic domain acts as a wedge at the branch point that splits parental/nascent duplexes while guiding displaced complementary strands into an annealing channel along the RecA-like motor domains.
Experiment: Perform single-molecule FRET assays on mobile Holliday junctions in the presence of UvsW, UvsX, gp32, and endonuclease VII (gp49).
Hypothesis: UvsW-driven branch migration displaces UvsX filaments and exposes open four-way junction conformations that either resolve by strand run-off or become licensed for gp49 endonucleolytic cleavage when branch migration stalls.
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