| Topic | Key points | Best supporting citations |
|---|---|---|
| Identity | - Target matches **mutL / PP_4896 / UniProt Q88DD1** in *Pseudomonas putida* KT2440, annotated as a DNA mismatch repair protein MutL.<br>- *P. putida* KT2440 carries **mutS** and **mutL** homologues but lacks **mutH** and Dam methylation, so it uses a MutH-independent MMR pathway.<br>- PP_4896 shares ~**44% amino-acid identity** with *E. coli* MutL, with stronger conservation in the N-terminal region. | Aparicio et al., 2020, *Environmental Microbiology*, Nov 2020, https://doi.org/10.1111/1462-2920.14814 (pqac-00000000, pqac-00000002) |
| Pathway role | - MutL functions in post-replicative **DNA mismatch repair (MMR)**, helping correct replication errors after base selection and proofreading.<br>- In *P. putida*, active MMR clearly depends at least on **MutS and MutL** and suppresses inheritance of ssDNA recombineering-generated mismatches.<br>- Transient inhibition of MutL allows mismatches to escape repair and become fixed as chromosomal mutations. | Fernández-Cabezón et al., 2021, *ACS Synthetic Biology*, Apr 2021, https://doi.org/10.1021/acssynbio.1c00031 (pqac-00000009); Aparicio et al., 2020, https://doi.org/10.1111/1462-2920.14814 (pqac-00000003, pqac-00000011) |
| Activities/domains | - Direct *P. putida*-specific biochemical assays were not provided in the retrieved papers, so ATPase/endonuclease activities are inferred from conserved bacterial MutL biology rather than demonstrated here.<br>- Authoritative review evidence indicates many MutL homologues in methylation-independent systems carry a **metal-dependent endonuclease motif** [DQHA(X)2E(X)4E].<br>- The same review indicates MutL activity is linked to the replication clamp **DnaN**, whose binding can stimulate MutL endonuclease activity in MutH-independent bacteria. | Wozniak & Simmons, 2022, *Nature Reviews Microbiology*, Feb 2022, https://doi.org/10.1038/s41579-022-00694-0 (pqac-00000005); Aparicio et al., 2020 discussion/citations, https://doi.org/10.1111/1462-2920.14814 (pqac-00000004) |
| Mismatch recognition hierarchy findings | - Using pyrF-targeted mutagenic ssDNA recombineering, the *P. putida* MMR hierarchy was reported as **A:G < C:C < G:A < C:A, A:A, G:G, T:T, T:G, A:C, C:T < G:T, T:C** from less to more sensitive to repair.<br>- Wild-type MMR therefore tolerates some mismatches much more than others; **G:T and T:C** are among the most strongly repaired.<br>- Transient expression of dominant-negative **mutL E36K** or permanent **ΔmutS** largely collapses this bias. | Aparicio et al., 2020, *Environmental Microbiology*, Nov 2020, https://doi.org/10.1111/1462-2920.14814 (pqac-00000002, pqac-00000010, pqac-00000011) |
| Mutator devices and phenotypes | - A dominant-negative **mutL<sub>E36K</sub>** allele was engineered in *P. putida* based on the equivalent inactive/dominant-negative *E. coli* allele; in KT2440 the homologous residue is **E36**.<br>- Regulated overexpression of **mutL<sub>E36K</sub>** on broad-host-range plasmids created conditional mutator devices that transiently inhibit endogenous MMR.<br>- These devices accelerated emergence of **streptomycin resistance, rifampicin resistance, dual antibiotic resistance, and reversion of a synthetic uracil auxotrophy**. | Aparicio et al., 2020, https://doi.org/10.1111/1462-2920.14814 (pqac-00000000, pqac-00000003); Fernández-Cabezón et al., 2021, https://doi.org/10.1021/acssynbio.1c00031 (pqac-00000001, pqac-00000007, pqac-00000008, pqac-00000009) |
| Quantitative mutation frequencies | - In the 2021 mutator-device study, inducible **mutL<sub>E36K</sub>** increased DNA mutation frequencies by **up to 438-fold** relative to controls.<br>- For uracil prototroph reversion, conditional mutator systems yielded about **750** and **860 Ura+ mutants per 1 × 10^9 viable cells** (cyclohexanone- and thermoinducible systems, respectively), whereas controls produced only **0–4** spontaneous Ura+ mutants under the tested conditions.<br>- In recombineering assays, wild-type MMR caused about a **two-orders-of-magnitude** difference between low-sensitivity (SR; A:G) and high-sensitivity (NR; G:T/C:A) oligos; this gap disappeared with **ΔmutS** or **mutL<sub>E36K</sub>** expression. | Fernández-Cabezón et al., 2021, *ACS Synthetic Biology*, Apr 2021, https://doi.org/10.1021/acssynbio.1c00031 (pqac-00000001, pqac-00000007, pqac-00000008, pqac-00000013, pqac-00000014); Aparicio et al., 2020, https://doi.org/10.1111/1462-2920.14814 (pqac-00000003, pqac-00000012) |
| Genome-wide off-target mutations | - Whole-genome sequencing of clones generated after transient **mutL<sub>E36K</sub>** expression found **0–3 SNPs** in edited strains.<br>- A control MMR-proficient strain analyzed in parallel showed **no detectable mutations**.<br>- These data support transient MutL inhibition as a practical genome-engineering strategy with relatively low off-target burden in *P. putida*. | Aparicio et al., 2020, *Environmental Microbiology*, Nov 2020, https://doi.org/10.1111/1462-2920.14814 (pqac-00000011) |


*Table: This table summarizes the most relevant functional annotation evidence for Pseudomonas putida KT2440 MutL, including pathway role, inferred activities, mismatch-recognition behavior, and engineering phenotypes. It is useful for distinguishing organism-specific findings from broader bacterial MutL inferences.*