Effective non-viral leader for cap-independent translation in a eukaryotic cell-free system.

The 61 nt 5'-untranslated region (5'-UTR) of mRNA encoding for a light-emitting protein of hydroid polyp Obelia longissima, obelin, is shown to provide a high level of cap-independent translation of heterologous mRNAs in cell-free translation systems based on wheat germ extracts. The inhibition of translation typically observed when excess mRNA is present or produced in a eukaryotic system (the so-called self-inhibition phenomenon) is found abated with mRNA constructs carrying the obelin mRNA leader. The role of the sequestration of a limiting initiation factor, probably eIF4F, in the self-inhibition phenomenon and the possible independence of the obelin mRNA leader from eIF4F are discussed. We propose the obelin mRNA leader be used for effective cap-independent translation in eukaryotic cell-free systems, including combined transcription-translation systems with uncontrolled phage polymerase-catalyzed accumulation of mRNA.

[Novel site-specific endonucleases F-TflI, F-TflII and F-TflIV encoded by the bacteriophage T5]. / Novye sait-spetsificheskie éndonukleazy F-TfI, F-TfII i F-TfIV, kodiruemye bakteriofagom T5.

Novel site-specific H-N-H endonucleases F-TflI, F-TflII and F-TflIV were identified. These endonucleases are encoded by open reading frames localized in the bacteriophage T5 tRNA gene region. The endonuclease F-TflIV was shown to introduce double-strand break into pseudo palindromic 17 bp DNA sequence yielding 1 bp extensions with 3'-overhangs. In contrast to F-TflIV, endonucleases F-TflI and F-TflII cleave only one strand of their asymmetric divergent DNA substrates. Each of these endonucleases introduces interruptions into only the particular strand (template or coding). Amino acid sequences of the endonucleases under study are highly homologous in the H-N-H motif regions and C-terminal sequences, forming putative catalytic domain. Endonuclease F-TflIV N-terminal region is homologous to the amino acid sequences representing H-T-H recognition domain found in LuxR family transcription regulators. Putative recognition NUMOD4 motif characteristic for a number of H-N-H endonucleases was shown to be also present in the endonuclease F-TflI and F-TflII N-terminal sequences. Two-domain structure was proposed for endonucleases F-TflI, F-TflII and F-TflIV with N-terminal recognition domain and C-terminal catalytic domain. A hypothesis of evolutionary origin of these endonucleases as a result of catalytic and recognition domains recombination was suggested.

Cotranslational formation of active photoprotein obelin in a cell-free translation system: direct ultrahigh sensitive measure of the translation course.

Translation of apoobelin mRNA in a cell-free wheat germ translation system in the presence of coelenterazine and molecular oxygen results in cotranslational formation of active photoprotein. Active obelin formation is recorded by its luminescence, either direct in the translation mixture in the presence of coelenterazine and calcium ions or in aliquots from the translation mixture. In the second case translation is carried out with coelenterazine and EGTA. Registration of the translation course by luminescence of the synthesized product in both cases allows use of apoobelin mRNA at very low concentrations as an internal marker for immediate measure of protein biosynthesis activity of in vitro translation systems. It is shown that the simultaneous translation of any other mRNA does not affect translation of photoprotein mRNAs under standard conditions. Continuous registration of luminescence in a cuvette of a liquid scintillation counter in photon-counting mode varies the time of signal accumulation in a wide temporal range, thus increasing the numerical values of the recorded signals. Registration of photoprotein luminescence during translation can be used to obtain additional information about the translation process, for example codon reading speed, about protein folding, and about the formation of active proteins on ribosomes.

[Stabilized reaction mixture for in vitro mRNA translation]. / Stabilizirovannaia reaktsionnaia smes' dlia transliatsii mRNK in vitro.

Here we describe a method for obtaining a ready-to-use stabilized reaction mixture for in vitro translation of mRNA. We also demonstrate the stabilization of a complete translation mixture containing wheat germ extract, amino acids, ATP, GTP, creatine phosphate, creatine kinase, and the reaction buffer by lyophilization in the presence of various sugars. The greatest stabilizing effect is achieved by supplementing the mixture with 10% (mass/volume) trehalose, which is also a unique translation activator, enhancing the translation of various mRNAs. A lyophilized complete translation mixture containing trehalose can be stored at 4-8 degrees C for several months without losing its activity. The mixture can be easily reconstituted by adding an aqueous mRNA solution and retains the potential for reproducible functioning. This allows the employment of such a cell-free translation system for analytical screening of a broad spectrum of compounds inhibiting translation at various stages.

Cell-free bioluminescent screening of translation inhibitors.

The possibility of creating new screening methods with a cell-free translation system has been demonstrated with a quantitative determination of diphtheria toxin and some antibiotics (puromycin, kanamycin and tetracycline) as examples. The approach proposed follows from the ability of various substances to inhibit protein synthesis. We used a wheat-germ cell-free translation system stabilized by freeze-drying in the presence of trehalose with the mRNA of the Ca(2+)-activated photoprotein obelin as a reporter template. This freeze-dried cell-free translation system allows prolonged storage of the detecting system before it is required, increases the reproducibility of the results and simplifies the application procedure. The obelin mRNA extends the sensitivity of the method owing to the high sensitivity of detection of the synthesized protein.

Effect of the ATP level on the overall protein biosynthesis rate in a wheat germ cell-free system.

A sensitive assay which examines the effects of ATP level on the overall activity of a cell-free translation system in a protein synthesis is described. The translational activity of cell-free system was measured in terms of a rate of protein synthesis directed by the 'test' template. The test template encodes a photoluminescent protein, obelin accumulation was determined from the kinetic curves of obelin. The rate of obelin mRNA translation. Time-dependent nucleotide level measurements were conducted throughout the translation processes. It has been shown that the rate of translation decreases exponentially with the decrease of the ATP level. This fall in the overall translation rate is due in part to the mRNA becoming inactive in the translation process. This is not caused by degradation, this mRNA can be restored for translation in a fresh cell-free system by phenol treatment. The reported results provide evidence that the level of ATP unambiguously determines the translational activity of the system.