GacA is the response regulator output of the GacS/GacA two-component regulatory system in Pseudomonas putida KT2440. Domain architecture and the conserved phosphoacceptor Asp54 support a phosphorelay-activated DNA-binding transcription regulator. In KT2440, the strongest direct evidence links the Gac system to transcriptional control of adhesin genes important for biofilm development, broader c-di-GMP-associated surface behaviors, and positive regulation of the K1 type VI secretion system.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000976 transcription cis-regulatory region binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: This is a reasonable computational annotation for a LuxR-family DNA-binding response regulator. The KT2440 literature does not yet provide direct promoter-binding data for GacA itself; the upstream-activating-sequence (UAS) binding evidence comes from P. fluorescens CHA0 and P. chlororaphis PA23 rather than KT2440. Domain architecture and transcriptional regulator function support retaining the term, but the indirect, homology-based nature of the evidence makes it non-core for the reviewed strain. Reason: The term is informative and consistent with the HTH LuxR-type output domain, but direct cis-regulatory-region binding has been demonstrated only in other pseudomonads, not in KT2440, so it is retained as non-core rather than as a core function. Supporting Evidence: file:PSEPK/gacA/gacA-uniprot.txt HTH luxR-type output domain and phosphoaccepting receiver domain identify GacA as a DNA-binding response regulator. file:PSEPK/gacA/gacA-notes.md Existing GOA terms for transcription-related DNA binding are directionally correct. file:PSEPK/gacA/gacA-deep-research-codex.md The broader Gac/Rsm model supports interpreting GacA as a phosphorelay-activated transcription regulator, but direct KT2440 promoter targets remain incompletely mapped. file:PSEPK/gacA/gacA-deep-research-falcon.md **GacA** as a **cytosolic response regulator** that, upon phosphorylation, acts as a DNA-binding transcription factor to activate transcription of sRNA genes. |
| GO:0003677 DNA binding | IEA GO_REF:0000002 | MODIFY | Summary: DNA binding is true for GacA, but this term is too broad to be a useful core annotation for a two-component transcription regulator. More informative replacements capture both the response-regulator nature of the protein and its role as a DNA-binding transcription factor. Reason: The annotation is correct in essence but overly general compared with more specific terms already supported by domain architecture and literature synthesis. Proposed replacements: phosphorelay response regulator activity DNA-binding transcription factor activity Supporting Evidence: file:PSEPK/gacA/gacA-uniprot.txt UniProt shows a response-regulator receiver domain, LuxR-type HTH domain, and phosphoacceptor Asp54. file:PSEPK/gacA/gacA-notes.md GO:0003677 DNA binding is too broad to be a useful core annotation for this protein. file:PSEPK/gacA/gacA-deep-research-codex.md The cleanest GO additions are therefore GO:0000156 phosphorelay response regulator activity and GO:0003700 DNA-binding transcription factor activity. file:PSEPK/gacA/gacA-deep-research-falcon.md GacA-family proteins are described as having an N-terminal receiver (REC) domain with a conserved phospho-accepting Asp and a C-terminal helix-turn-helix DNA-binding domain; this is consistent with the UniProt/InterPro assignment for Q88FJ6. |
| GO:0000160 phosphorelay signal transduction system | IEA GO_REF:0000002 | ACCEPT | Summary: This term captures a core and well-supported role of GacA as the response-regulator arm of a two-component phosphorelay. The receiver domain and conserved phosphoacceptor residue are consistent with classic phosphorelay signaling, and the KT2440 literature treats GacS/GacA explicitly as a functional two-component system. Reason: This is the central biological-process annotation for GacA and is directly aligned with both sequence architecture and experimental interpretation in KT2440 studies. Supporting Evidence: file:PSEPK/gacA/gacA-uniprot.txt Response-regulator receiver domain plus 4-aspartylphosphate at Asp54 support phosphorelay signaling. file:PSEPK/gacA/gacA-notes.md KT2440 literature consistently treats GacS/GacA as a two-component system governing surface-associated behaviors and other outputs. file:PSEPK/gacA/gacA-deep-research-codex.md The most defensible core picture for KT2440 is that GacA is a phosphorelay response regulator. file:PSEPK/gacA/gacA-deep-research-falcon.md GacA is the **response regulator** of the **GacS/GacA two-component system (TCS)**. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | MODIFY | Summary: GacA is clearly a transcription-related regulator, but the unsigned regulation term is broad and does not capture the directionality of GacA's activity. The falcon deep research establishes that activated GacA functions as a master transcriptional activator (it positively activates transcription of its direct targets, the Rsm-family sRNA genes), so a positive-regulation term is more informative and equally well supported. Reason: The annotation is correct in essence but unsigned; falcon synthesis shows GacA is specifically a transcriptional activator (master activator of sRNA genes), so the more informative GO:0045893 positive regulation of DNA-templated transcription is preferred over the generic regulation term. Proposed replacements: positive regulation of DNA-templated transcription Supporting Evidence: file:PSEPK/gacA/gacA-notes.md Current GOA terms for phosphorelay signal transduction and transcription-related DNA binding are directionally correct, but broad transcription-regulation terms are non-core. file:PSEPK/gacA/gacA-deep-research-codex.md The cleanest GO additions are core response-regulator and biofilm-regulation terms, while broader transcription-regulation terms are non-core. file:PSEPK/gacA/gacA-deep-research-falcon.md activated GacA is best understood as a **master transcriptional activator of small regulatory RNAs (sRNAs)** in the **Gac–Rsm pathway**, which then exerts broad post-transcriptional control through RNA-binding proteins. |
| GO:0000156 phosphorelay response regulator activity | IEA file:PSEPK/gacA/gacA-notes.md | NEW | Summary: This is the most informative molecular-function term for GacA. The protein is a canonical receiver/output response regulator with a conserved phosphoacceptor and a DNA-binding output domain. Supporting Evidence: file:PSEPK/gacA/gacA-uniprot.txt Response-regulator receiver domain, LuxR-type output domain, and phosphoacceptor Asp54 identify GacA as a phosphorelay response regulator. file:PSEPK/gacA/gacA-notes.md Phosphorelay response regulator activity is a better core molecular-function summary than generic DNA binding. file:PSEPK/gacA/gacA-deep-research-codex.md The most defensible core picture for KT2440 is that GacA is a phosphorelay response regulator. file:PSEPK/gacA/gacA-deep-research-falcon.md GacA-family proteins are described as having an N-terminal receiver (REC) domain with a conserved phospho-accepting Asp and a C-terminal helix-turn-helix DNA-binding domain; this is consistent with the UniProt/InterPro assignment for Q88FJ6. |
| GO:0003700 DNA-binding transcription factor activity | IEA file:PSEPK/gacA/gacA-notes.md | NEW | Summary: GacA should be represented as a DNA-binding transcription factor rather than only by generic DNA-binding and transcription-regulation terms. This term summarizes the protein's output role in the two-component regulatory system. Supporting Evidence: file:PSEPK/gacA/gacA-uniprot.txt The C-terminal LuxR-type HTH domain supports transcription factor activity. file:PSEPK/gacA/gacA-notes.md Literature and domain architecture support GacA as a DNA-binding transcription regulator, even though direct promoter targets remain incompletely mapped in KT2440. file:PSEPK/gacA/gacA-deep-research-codex.md The broader Gac/Rsm model supports interpreting GacA as a phosphorelay-activated transcription regulator. file:PSEPK/gacA/gacA-deep-research-falcon.md **GacA** as a **cytosolic response regulator** that, upon phosphorylation, acts as a DNA-binding transcription factor to activate transcription of sRNA genes. |
| GO:1900192 positive regulation of single-species biofilm formation | IEA file:PSEPK/gacA/gacA-notes.md | NEW | Summary: KT2440 and KT2442 literature directly connects the Gac system to adhesin-gene control and biofilm formation, making this the best supported specific biological-process term to add for the reviewed strain lineage. Supporting Evidence: file:PSEPK/gacA/gacA-notes.md The strongest direct KT2440 evidence places the Gac system upstream of adhesin expression and biofilm development. file:PSEPK/gacA/gacA-deep-research-codex.md The strongest direct KT2440 evidence links GacA to adhesin regulation, biofilm development, c-di-GMP-associated surface phenotypes, and positive regulation of the K1-T6SS. file:PSEPK/gacA/gacA-deep-research-falcon.md A well-defined *KT2440-specific* regulatory output of the Gac system is control of the large adhesins **LapA** and **LapF**, which function sequentially in biofilm development (LapA early adhesion; LapF later maturation). Both **lapA and lapF are under GacS/GacA control**. |
| GO:0005829 cytosol | IEA file:PSEPK/gacA/gacA-deep-research-falcon.md | NEW | Summary: GacA is a soluble cytosolic response regulator. Like other pseudomonad two-component response regulators, it lacks transmembrane segments or secretion signals and acts inside the cell as a DNA-binding transcription factor. A cytosol localization is a reasonable inferred cellular-component annotation. Supporting Evidence: file:PSEPK/gacA/gacA-deep-research-falcon.md **GacA** as a **cytosolic response regulator** that, upon phosphorylation, acts as a DNA-binding transcription factor to activate transcription of sRNA genes. |
Loading supporting content…
Download this section (compressed HTML)Q: Which KT2440 promoters or regulatory RNAs are direct binding targets of phosphorylated GacA?
Q: Is K1-T6SS control by GacA direct, or does it flow through Rsm, FleQ, RpoN, or other intermediate regulators?
Q: What environmental or physiological signals activate GacS/GacA during surface growth and interbacterial competition in KT2440?
Experiment: Construct an epitope-tagged functional GacA strain and perform ChIP-seq under planktonic, surface-grown, and stationary-phase conditions, ideally alongside a phosphomimetic or phosphodead allele to identify phosphorylation-dependent binding sites.
Hypothesis: GacA directly binds a limited set of promoters or sRNA loci that seed the broader KT2440 Gac regulon.
Type: ChIP-seq
Experiment: Compare RNA-seq profiles of wild type, gacA loss-of-function, gacS loss-of-function, and phosphosite-mutant gacA strains during planktonic growth, surface attachment, and late growth, then integrate with promoter-reporter assays for lapA, lapF, rpoS, and the K1-T6SS promoters.
Hypothesis: The biofilm and T6SS phenotypes attributed to GacA separate into direct and indirect branches of the regulon.
Type: RNA-seq and promoter-reporter analysis
Experiment: Complement a gacA mutant with wild-type, D54A, and D54E alleles and quantify biofilm biomass, lapA/lapF promoter activity, and K1-T6SS expression or competition phenotypes.
Hypothesis: Phosphorylation of Asp54 is required for the adhesin- and T6SS-regulatory outputs of GacA.
Type: targeted mutagenesis and phenotyping
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)