L-rhamnose-inducible expression systems
The present invention relates to methods for expressing nucleic acid sequences in prokaryotic host cells, where at least one DNA construct which is capable of episomal replication in a host cell and which comprises a nucleic acid sequence to be expressed under the transcriptional control of an L-rhamnose-inducible promoter, where the promoter is heterologous with regard to the nucleic acid sequence, is introduced into the host cell and the expression of he nucleic acid sequence is induced by addition of L-rhamnose, wherein the prokaryotic host cell is at least deficient with regard to an L-rhamnose isomerase.
1. A method for expressing nucleic acid sequences in prokaryotic host cells by high-density cell fermentation, comprising;
a) introducing into a prokaryotic host cell at least one DNA construct which is capable of episomal replication in said prokaryotic host cell and comprises a nucleic acid sequence to be expressed under the transcriptional control of an L-rhamnose-inducible promoter, wherein said L-rhamnose-inducible promoter is heterologous with regard to said nucleic acid sequence,
b) selecting prokaryotic host cells which comprise said DNA construct in episomal form, and
c) inducing the expression of said nucleic acid sequence by addition of L-rhamnose to a high-density cell culture of said selected prokaryotic host cells, wherein the concentration of L-rhamnose in the medium is from 0.01 g/l to 0.5 g/l,
wherein the prokaryotic host cell is at least deficient with regard to L-rhamnose isomerase.
2. The method according to claim 1 . wherein the prokaryotic host cell is selected from the species of the family Enterobacteriaceae or the order Actinomycetales.
3. The method according to claim 1 , wherein the prokaryotic host cell is Escherichia coli.
4. The method of claim 1 , wherein the L-rhamnose-inducible promoter is the rhaP BAD promoter from E. coli.
5. The method of claim 1 , wherein the L-rhamnose-inducible promoter comprises at least one RhaS binding element as shown in SEQ ID NO: 5.
6. The method of claim 1 , wherein the L-rhamnose-inducible promoter comprises at least one sequence described by SEQ ID NO: 1, 2, 3 or 4.
7. The method according to claim 1 , wherein the L-rhamnose isomerase comprises the amino acid sequence of SEQ ID NO: 9.
8. The method according to claim 1 , wherein the DNA construct which is capable of episomal replication has a size of not more than 100,000 bases or base pairs.
9. The method according to claim 1 , wherein the DNA construct which is capable of episomal replication is selected from the group consisting of circular plasmid vectors, phagemids and cosmids.
10. The method according to claim 1 , wherein the prokaryotic host cell has at least one further deficiency with regard to a gene which has a function in the metabolization of rhamnose, where said gene encodes a protein selected from the group consisting of rhamnulose 1-phosphatase (RhaB) and rhamnulose-phosphate aldolase (RhaD).
11. The method according to claim 1 , wherein the expression of the nucleic acid sequence to be expressed causes the production of a protein encoded by said nucleic acid sequence.
12. The method according to claim 1 , wherein the nucleic acid sequence to be expressed encodes a recombinant protein selected from the group consisting of chymosines, proteases, polymerasen, saccharidases, dehydrogenases, nucleases, glucanases, glucose oxidases, α-amylases, oxidoreductases, peroxidases, laccases, xylanases, phytases, cellulases, collagenases, hemicellulases, lipases, lactases. pectinases, amyloglucosidases, glucoamylases, pullulanases, glucose isomerases, nitrilases, esterases, nitrile hydratases, amidases, oxygenases, oxynitrilases, lyases, lactonases, carboxylases, collagenases, cellulases, serum albumins, factor VII, factor VIll, factor IX, factor X, tissue plasminogen factors, protein C, von Willebrand factors, antithrombins. erythropoietins, colony-stimulating factors. cytokins, interleukins, insulins, integrins, addressins, selectins, antibodies, antibody fragments, structural proteins, collagen, fibroins, elastins, tubulins, actins, myosins, growth factors, cell-cycle proteins, vaccines, fibrinogens and thrombins.
13. An isolated prokaryotic host cell capable of producing recombinant proteins by high-density cell fermentation, wherein said host cell is at least deficient with regard to L-rhamnose isomerase and comprises at least one DNA construct, wherein the at least one DNA construct is capable of replication in said host cell and comprises a nucleic acid sequence to be expressed under the transcriptional control of an L-rhamnose-inducible promoter in the presence of L-rhamnose at a concentration from 0.01 g/l to 0.5 g/l in high-density cell fermentation, wherein said L-rhamnose-inducible promoter is heterologous with regard to said nucleic acid sequence.
14. A process for the production of foodstuffs, feedstuffs, enzymes, chemicals, pharmaceuticals or fine chemicals, which comprises culturing the isolated prokaryotic host cell of claim 13 under high-density cell culture conditions allowing expression of said nucleic acid sequence for preparing foodstuffs, feedstuffs, enzymes, chemicals, pharmaceuticals or fine chemicals, and isolating the foodstuffs, feedstuffs, enzymes, chemicals, pharmaceuticals or fine chemicals produced.
15. A method for the production of recombinant proteins, enzymes or fine chemicals, comprising culturing the isolated prokaryotic host cell of claim 13 under high-density cell culture conditions allowing expression of said nucleic acid sequence for producing recombinant proteins, enzymes and fine chemicals, and isolating the recombinant proteins, enzymes and fine chemicals produced.