Continuously coupled transcription-translation system for the production of rice cytoplasmic aldolase

Cell-free protein synthesis at high temperatures using the lysate of a hyperthermophile

Systems for cell-free protein synthesis available today are usually based on the lysates of either Escherichia coli, wheat germ or rabbit reticulocyte, and protein synthesis reactions using these extracts are performed at moderate temperatures (20-40 degrees C). We report here the development of a novel system for cell-free protein synthesis that can be operated at high temperatures using a lysate of the hyperthermophilic archaeon, Thermococcus kodakaraensis. With the system, cell-free protein synthesis of ChiADelta4, a derivative of T. kodakaraensis chitinase (ChiA), was observed within a temperature range of 40-80 degrees C, with an optimum at 65 degrees C. Corresponding chitinase activity was also detected in the reaction mixtures after cell-free protein synthesis, indicating that the synthesized ChiADelta4 folded in a proper tertiary structure. The maximum concentration of active ChiADelta4 synthesized was determined to be approximately 1.3 microg/mL. A time course experiment indicated that the amount of synthesized ChiADelta4 saturated within 30 min at 65 degrees C, and energy depletion was suggested to be the main cause of this saturation. We further developed a system for transcription and translation-coupled protein synthesis at high temperatures using a combination of T. kodakaraensis lysate and thermostable T7 RNA polymerase.

Recent advances in producing and selecting functional proteins by using cell-free translation

Prokaryotic and eukaryotic in vitro translation systems have recently become the focus of increasing interest for tackling fundamental problems in biochemistry. Cell-free systems can now be used to study the in vitro assembly of membrane proteins and viral particles, rapidly produce and analyze protein mutants, and enlarge the genetic code by incorporating unnatural amino acids. Using in vitro translation systems, display techniques of great potential have been developed for protein selection and evolution. Furthermore, progress has been made to efficiently produce proteins in batch or continuous cell-free translation systems and to elucidate the molecular causes of low yield and find possible solutions for this problem.

Cell-free protein synthesis systems

Cell-free protein synthesis systems enable the direct in vitro expression of proteins from template DNA or RNA. Use of biochemical and bioengineering techniques has greatly improved the yields and productivities of cell-free systems. In some cases, the yields approach the in vivo levels. Moreover, in vitro systems are capable of rapidly providing artificial polypeptides that greatly facilitate protein engineering. Post-translational modification steps in cell-free systems also offer exciting possibilities as reviewed here.

Translation in plants--rules and exceptions

Translation processes in plants are very similar to those in other eukaryotic organisms and can in general be explained with the scanning model. Particularly among plant viruses, unconventional mRNAs are frequent, which use modulated translation processes for their expression: leaky scanning, translational stop codon readthrough or frameshifting, and transactivation by virus-encoded proteins are used to translate polycistronic mRNAs; leader and trailer sequences confer (cap-independent) efficient ribosome binding, usually in an end-dependent mechanism, but true internal ribosome entry may occur as well; in a ribosome shunt, sequences within an RNA can be bypassed by scanning ribosomes. Translation in plant cells is regulated under conditions of stress and during development, but the underlying molecular mechanisms have not yet been determined. Only a small number of plant mRNAs, whose structure suggests that they might require some unusual translation mechanisms, have been described.

Dihydrofolate reductase synthesis in the presence of immobilized methotrexate. An approach to a continuous cell-free protein synthesis system

Dihydrofolate reductase was synthesized in a batch system in the presence of the affinity ligand methotrexate, bound to various matrices. Two types of gel were used: commercial methotrexate-agarose with pores inaccessible for translation machinery and methotrexate-POROS with pores easily accessible for translation reaction mixture components. The transcription/translation reaction was not inhibited by either the immobilized methotrexate or the matrix. The enzyme was synthesized with a high yield and could simultaneously be removed from the reaction mixture by the affinity matrix during the synthesis. With methotrexate-POROS present the reaction probably proceeded mainly in the pores of the gel. Kinetic limitations to the reaction in the presence of the gel were not observed. Active dihydrofolate reductase was eluted from methotrexate-POROS. The activity recovered was higher than dihydrofolate reductase activity synthesized in free solution system. The influence of the presence of immobilized methotrexate on dihydrofolate reductase synthesis will be further studied in a novel type of a continuous protein synthesis system.