| Topic | Key takeaways | Most relevant paper | DOI URL |
|---|---|---|---|
| Identity/domains | UniProt Q88DD3 corresponds to **Hfq** in *Pseudomonas putida* KT2440 (gene **hfq**, locus **PP_4894**). Hfq is a conserved **bacterial Sm/Lsm-family** RNA-binding protein with a conserved **Sm domain**, typically forming a **homohexameric ring** with proximal, distal, rim, and C-terminal RNA-interaction regions; in *Pseudomonas*, Hfq is described as a **hexameric RNA-binding protein** central to post-transcriptional regulation. (pqac-00000003, pqac-00000004, pqac-00000017) | Huber, 2021, Dissertation; Pusic et al., 2021, *Int. J. Mol. Sci.*; Hernández-Arranz et al., 2016, *RNA* | https://doi.org/10.5282/edoc.27581; https://doi.org/10.3390/ijms22168632; https://doi.org/10.1261/rna.058313.116 |
| Core molecular function | Hfq is an **RNA chaperone / molecular matchmaker** that stabilizes sRNAs, accelerates **sRNA–mRNA base pairing**, can directly repress translation near RBSs, and can recruit or facilitate RNase-mediated decay; in *Pseudomonas*, it is a global post-transcriptional regulator affecting metabolism and stress-related functions. (pqac-00000000, pqac-00000003, pqac-00000004) | Huber, 2021, Dissertation; Hernández-Arranz et al., 2016, *RNA* | https://doi.org/10.5282/edoc.27581; https://doi.org/10.1261/rna.058313.116 |
| CCR with Crc/CrcZ/CrcY | In *P. putida*, Hfq cooperates with **Crc** to form repressive complexes on target mRNAs carrying **A-rich CA motifs** (consensus **AAnAAnAA**), inhibiting translation of catabolic genes. **CrcZ** and **CrcY** antagonize repression by sequestering Hfq/Crc; **Crc and Hfq increase CrcZ stability**, and processed **CrcZ\*** can relieve hyperrepression in a ΔcrcZΔcrcY background. (pqac-00000000, pqac-00000001, pqac-00000017, pqac-00000018, pqac-00000022) | Hernández-Arranz et al., 2016, *RNA* | https://doi.org/10.1261/rna.058313.116 |
| RNA cycling/scanning mechanisms | Recent mechanistic work (not KT2440-specific, but on conserved Hfq action) shows Hfq binds **(ARN)n** motifs with diffusion-limited on-rates, compacts RNA, and uses **rim arginines** to support iterative **1D scanning/hopping** and transfer of sRNAs between sites without dissociation, enabling kinetic selection of optimal duplexes. This refines current understanding of how Hfq accelerates target search. (pqac-00000008, pqac-00000010, pqac-00000012, pqac-00000014, pqac-00000029, pqac-00000030) | Małecka & Woodson, 2024, *Nature Communications*; Rodgers et al., 2023, *Molecular Cell* | https://doi.org/10.1038/s41467-024-46316-6; https://doi.org/10.1016/j.molcel.2023.04.003 |
| Localization | The current evidence snippets support Hfq as a **cytoplasmic RNA-binding/post-transcriptional regulator** acting on mRNAs and sRNAs; however, **no KT2440-specific subcellular localization experiment** is provided in the retrieved evidence. Thus, localization should be annotated conservatively as **intracellular/cytoplasmic RNA-associated**, inferred from mechanism rather than direct KT2440 localization data. (pqac-00000000, pqac-00000003, pqac-00000004) | Huber, 2021, Dissertation; Hernández-Arranz et al., 2016, *RNA* | https://doi.org/10.5282/edoc.27581; https://doi.org/10.1261/rna.058313.116 |
| Applications/engineering | The Hfq-linked CCR network has practical value in **metabolic engineering** of *P. putida*. Overexpressing **CrcY/CrcZ** in KT2440 boosts **medium-chain-length PHA** production and alters polymer molecular weight, showing that tuning Hfq/Crc decoy sRNAs can reprogram carbon flux for bioproduct formation. Broader reviews also point to impacts on bioremediation-relevant catabolism. (pqac-00000024, pqac-00000025, pqac-00000026, pqac-00000027, pqac-00000028) | Che et al., 2025, *Biotechnology for Biofuels and Bioproducts* | https://doi.org/10.1186/s13068-025-02707-5 |
| Quantitative data | Reported figures include: Hfq has **~5–20-fold higher affinity for CrcZ than for amiE mRNA**; in WT, ~**20%** of crcZ signal was TEX-sensitive, indicating processed forms; overexpressing CrcY/CrcZ increased PHA titers by **1.3–3.5-fold**, with examples including **0.34 vs 0.15 g/L**, **0.67–0.77 vs 0.51 g/L**, and **63% CDW (0.57 g/L) vs 33% CDW (0.17 g/L)**; deleting both sRNAs caused a **2.5-fold decrease** in PHA; polymer **Mw** decreased from **2.228×10^5 to 9.468×10^4 g/mol** in one overexpression condition. Conserved Hfq mechanism studies measured **39%** shuttling events for N=13 vs **23%** for N=35 spacers and **2.8** vs **1.6** transitions/event. (pqac-00000018, pqac-00000021, pqac-00000024, pqac-00000025, pqac-00000026, pqac-00000008, pqac-00000030) | Pusic et al., 2021, *Int. J. Mol. Sci.*; Che et al., 2025, *Biotechnology for Biofuels and Bioproducts*; Małecka & Woodson, 2024, *Nature Communications* | https://doi.org/10.3390/ijms22168632; https://doi.org/10.1186/s13068-025-02707-5; https://doi.org/10.1038/s41467-024-46316-6 |


*Table: This table summarizes identity, mechanism, CCR function, localization, applications, and key quantitative findings for *Pseudomonas putida* KT2440 Hfq (hfq/PP_4894; UniProt Q88DD3). It is designed as a concise evidence-backed insert for the research report.*