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Results for “tuneable promoter”

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PubMed2025

A new tool for engineering Phaeodactylum tricornutum: the METE promoter drives both high expression and B12-tuneable regulation of transgenes.

For advanced metabolic engineering strategies, it is crucial to be able to regulate transgene expression, to prevent potential deleterious effects in the host organism during growth and allow optimisation of production levels. Here, we identified vitamin B12 (cobalamin)-responsive promoters in the diatom Phaeodactylum tricornutum, a promising biotechnological chassis that readily absorbs this metabolite with minimal physiological impact. Using promoter-reporter constructs, the promoters of the cobalamin acquisition protein 1 (CBA1) and the B12-independent form of methionine synthase (METE) were shown to regulate transgene expression in a B12-dependent manner. Further characterisation of the METE promoter (PMETE) demonstrated that it exhibited significantly higher expression levels than several previously characterised promoters, but could be repressed by nanomolar amounts of B12, with a dynamic range >100-fold. Tight regulation was demonstrated by the suppression of the lethal ribonuclease, barnase at 1 μg L-1 B12. Reporter expression was doubled when PMETE was paired with its cognate terminator, compared with the widely used FCPA terminator. Promoter truncations resulted in decreased expression, but no loss of B12 regulation. A 14 nucleotide motif, present in four copies in PMETE, was found to be necessary for expression, and when fused to the constitutive FCPA promoter, enhanced expression levels. Transgenic lines expressing the heterologous diterpenoid enzyme, casbene synthase, produced casbene titres of approximately 2 mg L-1 and this was tuneable by B12. This demonstrates the utility of PMETE in efforts to establish P. tricornutum as an industrial biotechnology production platform.

Promoter Regions, Genetic↗

PubMed2006

Energy transfer in thermal and hyperthermal collisions between CN(X2Sigma+, v = 2) in selected rotational levels (Ni = 0, 1, 6, 10, 15 and 20) and N2.

We report rate coefficients (k(tot,N(i))) for total removal of CN(X(2)Sigma(+), v = 2, N(i)) radicals from selected rotational levels (N(i) = 0, 1, 6, 10, 15 and 20) and for state-to-state rotational energy transfer (k(i-->f)) between levels N(i) and other rotational levels N(f) in single collisions with N(2). CN radicals have been generated using two sources: (a) the pulsed laser photolysis of ICN at 266 nm, which generates translationally 'hot' CN radicals; and (b) the pulsed laser photolysis of NCNO at 570 nm, which generates CN radicals with translational energies close to the average value at 298 K. Comparison of the values of k(tot,N(i)) obtained using these two sources of CN demonstrates: firstly, that the same results are obtained as long as time is allowed for the translationally hot CN radicals generated from ICN to be thermalised before radicals are promoted to a specific rotational level in v = 2 using a tuneable infrared 'pump' laser operating at ca. 2.45 micro m; and secondly, that the rate coefficients decrease, but the averaged cross-sections remain approximately constant, as the excess translational energy in CN radicals is moderated by collisions. With NCNO as the source of CN radicals, the observed values of k(tot,N(i)) do not depend on the delay between the pulses from the photolysis and pump lasers. Finally, we demonstrate that, for the non-reactive collision partner N(2) and with allowances made for the rate coefficients that are too small to measure directly, the sum of the state-to-state rate coefficients, Sigma(f)k(i-->f), for rotational energy transfer from a selected initial level N(i) agrees quite well with the value of k(tot,N(i)) for total transfer from the same initial level. The values of k(tot,N(i)) and of the state-to-state rate coefficients are compared with similar, earlier, results in which helium and argon were the collision partners. The relevance of these results to the study of collisions of CN with reactive collision partners is briefly discussed.

Chemical Phenomena↗

PubMed1997

Crosslinking of progesterone receptor to DNA using tuneable nanosecond, picosecond and femtosecond UV laser pulses.

UV laser crosslinking is a potentially powerful tool to investigate transient DNA-protein interactions and binding kinetics in intact cells. As the processes underlying UV laser crosslinking are not fully understood, we have performed a study of the influence of laser pulses with different physical parameters on crosslinking of the progesterone receptor to an oligonucleotide containing a hormone-responsive element. We also studied the influence of the various parameters on the amount of laser-irradiated DNA that can be correctly primer extended as an operational measurement of DNA integrity. A strong influence of pulse intensity and pulse length on the crosslink yield was found, likely due to a change in the 'two photon' processes responsible for crosslinking. The highest efficiency of protein crosslinking to DNA was achieved with femtosecond pulses and should be sufficient to enable use of this technique for in vivo studies.

Animals↗