SummaryTn 4430 is a distinctive transposon of the Tn 3 family that encodes a tyrosine recombinase (TnpI) to resolve replicative transposition intermediates. The internal resolution site of Tn 4430 (IRS, 116 bp) contains two inverted repeats (IR1 and IR2) at the crossover core site, and two additional TnpI binding motifs (DR1 and DR2) adjacent to the core. Deletion analysis demonstrated that DR1 and DR2 are not required for recombination in vivo and in vitro . Their function is to provide resolution selectivity to the reaction by stimulating recombination between directly oriented sites on a same DNA molecule. In the absence of DR1 and/ or DR2, TnpI-mediated recombination of supercoiled DNA substrates gives a mixture of topologically variable products, while deletion between two wild-type IRSs exclusively produces two-noded catenanes. This demonstrates that TnpI binding to the accessory motifs DR1 and DR2 contributes to the formation of a specific synaptic complex in which catalytically inert recombinase subunits act as architectural elements to control recombination sites pairing and strand exchange. A model for the organization of TnpI/IRS recombination complex is presented.

In DNA site-specific recombination catalysed by tyrosine recombinases, two pairs of DNA strands are sequentially exchanged between separate duplexes and the mechanisms that confer directionality to this theoretically reversible reaction remain unclear. The tyrosine recombinase TnpI acts at the internal resolution site (IRS) of the transposon Tn4430 to resolve intermolecular transposition products. Recombination is catalysed at the IRS core sites (IR1–IR2) and is regulated by adjacent TnpI-binding motifs (DR1 and DR2). These are dispensable accessory sequences that confer resolution selectivity to the reaction by stimulating synapsis between directly repeated IRSs. Here, we show that formation of the DR1–DR2-containing synapse imposes a specific order of activation of the TnpI catalytic subunits in the complex so that the IR1-bound subunits catalyse the first strand exchange and the IR2-bound subunits the second strand exchange. This ordered pathway was demonstrated for a complete recombination reaction using a TnpI catalytic mutant (TnpI-H234L) partially defective in DNA rejoining. The presence of the DR1- and DR2-bound TnpI subunits was also found to stabilize transient recombination intermediates, further displacing the reaction equilibrium towards product formation. Implication of TnpI/IRS accessory elements in the initial architecture of the synapse and subsequent conformational changes taking place during strand exchange is discussed.

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BackgroundReal-world evidence on effectiveness and safety data for patients (pts) with psoriatic arthritis (PsA) in the Belgium clinical practice setting is lacking.ObjectivesTo assess the effectiveness and safety of apremilast (APR) in pts with active PsA from routine clinical practice in Belgium.MethodsIn this multicentre, prospective, non-interventional study (APOLO), the PsA Response Criteria (PsARC) response 6 months after aPR initiation was the primary endpoint. PsARC response was defined as improvement in ≥2 and no worsening of any of the following 4 measures: tender joint count (TJC; 0-68), swollen joint count (SJC; 0-66), Physician’s Global assessment of Disease activity (PhGA) and Patient’s Global assessment of Disease activity (PtGA). Other endpoints included PsAID12, HAQ-DI, Physician’s and Patient’s Numerical Rating Scale (NRS) assessing disease activity for the most affected joint, psoriasis-affected body surface area (BSA), enthesitis, dactylitis, pain and pruritus. The current analysis is based on observed data.ResultsThe first 55 of a planned 150 Belgian pts receiving aPR for up to 6 months were evaluated. Mean age was 52.5 yrs, mean BMI was 27.1 kg/m2 and 47.3% were female. Mean durations of psoriasis and PsA were 15.8 yrs and 8.1 yrs, respectively; ≈80% of pts were biologic-naive. At baseline (BL), mean (SD) SJC was 8.0 (5.4), mean (SD) TJC was 12.7 (9.5) and mean (SD) body surface affected was 12.3% (20.8%); 31.0% of pts had dactylitis and 47.8% had enthesitis. In total, 35 pts (63.6%) continued aPR treatment for 6 months; 20 (36.4%) had discontinued aPR (insufficient effectiveness: 21.8%; adverse events: 10.9%, intolerance: 3.6%). After 6 months of aPR initiation, 69.6% of pts had a PsARC response. Mean changes from BL in SJC were −4.4 (Month 3) and −5.7 (Month 6), with improvements in SJC (defined as ≥30% decrease per PsARC) observed in most pts (Month 3: 78.3%; Month 6: 83.3%). Comparable results were seen for TJC: Mean changes from BL were −7.2 (Month 3) and −6.7 (Month 6), with improvements observed in most pts (Month 3: 78.3%; Month 6: 80%). Decreases in PhGA score of ≥1 from BL were observed in most pts at Months 3 (73.7%) and 6 (66.7%). Mean (SD) Physician’s NRS scores decreased from 5.6 (2.6) at BL to 2.5 (2.0) at Month 6. Among pts with enthesitis at BL who had data available at Month 6, 54.5% achieved a score of 0. Among pts with dactylitis at BL who had data available at Month 6, 44.4% achieved a score of 0. BL mean (SD) PsAID12 score of 5.9 (1.6) decreased to 3.7 (1.8) at Month 6. Mean (SD) BSA improved from 12.3% (20.8%) at BL to 7.5% (14.7%) at Month 6. An improvement of ≥20% in HAQ-DI at Month 6 was achieved by 73.1% of pts. Improvements were also seen in PtGA score, overall pain and pruritus. No new safety and tolerability concerns from known overall safety profile of aPR.ConclusionResults from this real-world PsA study confirmed an improvement in disease activity with aPR in both physician-assessed and pt-reported outcomes for most pts. Overall, improvements were observed afte...