The review target requested as gacA in Pseudomonas putida KT2440 maps to UniProt Q88FJ6. UniProt records the gene name as uvrY, the ordered locus name as PP_4099, and the protein name as "Response regulator GacA (Global activator)." The protein is 212 aa long and contains a receiver domain plus a C-terminal LuxR-type helix-turn-helix output domain, with a predicted phosphoacceptor Asp54. This is the expected architecture of a transcriptionally acting two-component response regulator. [file:PSEPK/gacA/gacA-uniprot.txt "RecName: Full=Response regulator GacA"] [file:PSEPK/gacA/gacA-uniprot.txt "DOMAIN 3..119"] [file:PSEPK/gacA/gacA-uniprot.txt "DOMAIN 141..206"] [file:PSEPK/gacA/gacA-uniprot.txt "MOD_RES 54"]
The most direct KT2440 evidence ties the Gac system to transcriptional control of the two major adhesin loci lapA and lapF, which organize the transition from early attachment to mature biofilm architecture. The key KT2440 paper states that both adhesin genes are controlled by GacS/GacA and describes the system as a master regulator of the biofilm program. PMID:24488315 PMID:24488315
Independent support comes from a KT2442 mutant screen, where a gacS insertion produced a moderate biofilm defect. That does not isolate GacA biochemically, but it reinforces that the same two-component system contributes to biofilm development in the lab strain lineage. PMID:27190143
In KT2440, a genetic dissection of the high-c-di-GMP crinkly-colony phenotype recovered GacA as one of the global regulators needed for the lifestyle shift associated with elevated c-di-GMP. This places GacA in the regulatory network that connects phosphorelay signaling to surface-associated behavior. PMID:27489550
The same paper also notes that GacS/GacA is essential for rpoS expression in KT2440, offering a mechanistic route by which GacA can influence broad stationary-phase and biofilm-associated outputs even when direct GacA promoter binding has not yet been mapped. PMID:27489550
More recent KT2440 work extends the GacA regulon beyond biofilm-associated genes. The K1 type VI secretion system (T6SS), which supports interbacterial competition and plant-protective activity, is positively regulated by GacS-GacA and repressed by RetS. This indicates that GacA is part of a broader lifestyle-control module spanning both surface colonization and contact-dependent antagonism. PMID:36748579
The broader Gac/Rsm literature describes GacA/UvrY proteins as phosphorelay-activated transcription regulators that trigger expression of one or more small RNAs, which then sequester Rsm/Csr translational repressors. This is the standard mechanistic framework for interpreting GacA-like regulators across gamma-proteobacteria. PMID:18047567 PMID:11768529
For KT2440 specifically, this framework is highly plausible, but I did not find direct evidence in the examined papers that identifies the precise small RNA promoters or demonstrates purified GacA binding to a defined target promoter. Because of that gap, the safest curation stance is:
phosphorelay signal transduction systemphosphorelay response regulator activityOther P. putida strains show the same regulatory module governing quorum sensing, cyclic lipopeptide biosynthesis, and carbon-storage/polymer phenotypes:
ppuI quorum-sensing synthase. PMID:15345437These strain-level observations strengthen the interpretation of GacA as a pleiotropic lifestyle regulator, but they should not automatically be converted into KT2440-specific GO terms without direct support in the KT2440 lineage.
The most defensible core picture for KT2440 is that GacA is a phosphorelay response regulator and DNA-binding transcription regulator upstream of biofilm-associated adhesin control, c-di-GMP-linked surface behavior, and at least one antagonistic output (K1-T6SS). The cleanest GO additions are therefore GO:0000156 phosphorelay response regulator activity, GO:0003700 DNA-binding transcription factor activity, and GO:1900192 positive regulation of single-species biofilm formation, while keeping broader transcription-regulation terms as non-core.
rsmY/rsmZ-type RNAs versus additional regulators is not clear from the examined literature.