Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Recombinant dna technique included in method of making a...
Patent
1994-05-20
1997-01-14
Ketter, James S.
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Recombinant dna technique included in method of making a...
435 693, 435 694, 435 6951, 435 6952, 435 696, 435183, 4352542, 4353201, C12P 2102, C12N 115, C12N 1581
Patent
active
055938582
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of biotechnology, and more particularly to that of industrial fermentations by recombinant microorganisms.
Still more particularly, it relates to a host/vector pair which is highly stable in a complex medium, its preparation and its use in industrial fermentation.
The advances accomplished in the field of molecular biology have made it possible to modify microorganisms in order to make them produce specific recombinant proteins, preferably heterologous proteins. In particular, numerous genetic studies have been performed on the bacterium E. coli. More recently, yeasts such as Saccharomyces, Kluyveromyces, Pichia, or even Hansenula, have emerged as promising host organisms for this mode of protein production.
However, the industrial application of these new modes of production is still limited, especially by the problems of the efficacy of gene expression in these recombinant microorganisms, and by the difficulty of obtaining recombinant cells which are stable under industrial fermentation conditions. One of the essential operational constraints is indeed linked to the segregational stability of an expression vector inside the host used. At the industrial level, a vector should possess a high stability over at least 25 successive generations, which approximately represent the number of generations required to go as far as the end of a 200-m.sup.3 fed batch-type industrial fermenter (Principles of Fermentation Technology, Stanburry and Whitaker, Pergamon Press, Oxford, 1984). The stability of the vector must be even higher in the case of continuous fermentation where it must reach not less than about one hundred generations.
In bacteria, the most common solution used in the laboratory consists of inserting a gene for resistance to an antibiotic into the plasmid used, which endows the bacteria with the capacity to survive and grow in a selective medium containing said antibiotic. However, because of security and regulatory constraints in the field of biotechnology, it is essential to be able to avoid the use of antibiotic resistance genes at the industrial level. In yeasts, the most commonly used method consists of culturing cells with a defective pathway for the biosynthesis of amino acids (Trp, Leu, His) or of purine (adenine) or pyrimidine (uracil) bases, said cells being transformed by a vector containing a gene which is capable of complementing this defect. However, this approach requires the use of media lacking the amino acid or the base for which the host strain is auxotrophic. The use of such synthetic media has numerous disadvantages. In particular, these media are expensive, which is incompatible with an industrial use, and furthermore, they lead to slower growth of the cells and to a smaller biomass.
A solution has been proposed to avoid the use of a synthetic medium or of antibiotic resistance genes, which consists of (i) mutating a gene which is essential for survival in a complex medium in the host cell and (ii) introducing an intact copy of said gene into the expression plasmid used. This system, the principle of which is to force the host cell to retain its plasmid, has enabled the stability of the host/vector pair to be increased. This system has, in particular, been described for E. coli, for the dapD gene which encodes tetrahydropicolinate-N-succinyl transferase (EP 258 118), for the valS gene whose product is an enzyme which is required for protein synthesis (Skogman and Nilsson, Gene 31 (1984) 117), and for the ssb gene whose product is essential for DNA replication and for the survival of the cell (Porter et al., Bio/technology vol. 8 (1990) 47). Ferrari et al. have also described the use of the racemase alanine gene for stabilising a plasmid inside a B. subtilis mutant in which this gene was not functional (Bio/technology vol. 3 (1985) 1003). Application WO 86/01224 describes a similar selection system which is suitable for the yeast S. cerevisiae. This system uses the yeast S. cerevisiae which has a mutation in 2 genes which are involved in t
REFERENCES:
patent: 4857467 (1989-08-01), Sreekrishna et al.
Nucleic Acids Res. 18(17):5294, 1990 Goffrini et al., "RAG1 Gene of the Yeast Kluyveromyces lactis Codes for a Sugar Transporter".
Fournier et al., Nuc. Acids Res., vol. 18, 1990, p. 365.
Rothstein, Methods in Enzymology, vol. 101, 1983, pp. 202-211.
Ohya et al., Genetics, vol. 138, 1994, pp. 1041-1054.
Fleer Reinhard
Fournier Alain
Yeh Patrice
Ketter James S.
Rhone-Poulenc Rorer SA
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