Inducible coexpression system

1. An Escherichia coli host cell comprising two or more types of expression constructs,

wherein the expression construct of each type comprises an inducible promoter and a polynucleotide sequence encoding a gene product to be transcribed from the inducible promoter; and

at least one of said inducible promoters is responsive to an inducer that is different than the inducer of another of said inducible promoters; and

each inducible promoter is selected from the group consisting of: an L-arabinose-inducible promoter, a propionate-inducible promoter, a rhamnose-inducible promoter, and a D-xylose-inducible promoter; and

wherein the host cell has a reduced level of gene function of at least one gene encoding a protein that metabolizes an inducer of at least one said inducible promoter; and

wherein the host cell has a reduced level of gene function of a gene that encodes a reductase; and

at least one of said gene products forms a multimer with another of said gene products; and

at least one of said gene products is a polypeptide that lacks a signal peptide.

2. An Escherichia coli host cell comprising two or more types of expression constructs,

wherein the expression construct of each type comprises an inducible promoter and a polynucleotide sequence encoding a gene product to be transcribed from the inducible promoter; and

at least one of said inducible promoters is responsive to an inducer that is different than the inducer of another of said inducible promoters; and

each inducible promoter is selected from the group consisting of: an L-arabinose-inducible promoter, a propionate-inducible promoter, a rhamnose-inducible promoter, and a D-xylose-inducible promoter; and

wherein the host cell has a reduced level of gene function of at least one gene encoding a protein that metabolizes an inducer of at least one said inducible promoter; and

wherein the host cell has a reduced level of gene function of a gene that encodes a reductase; and

at least one of said gene products is a polypeptide that lacks a signal peptide.

3. The host cell of claim 2 wherein at least one inducible promoter is an L-arabinose-inducible promoter.

4. The host cell of claim 2 wherein at least one inducible promoter is a propionate-inducible promoter.

5. The host cell of claim 2 wherein at least one inducible promoter is selected from the group consisting of: the araBAD promoter, the prpBCDE promoter, the rhaSR promoter, and the xlyA promoter.

6. The host cell of claim 2 wherein at least one expression construct further comprises a polynucleotide sequence encoding a transcriptional regulator that binds to an inducible promoter.

7. The host cell of claim 6 wherein the polynucleotide sequence encoding a transcriptional regulator and the inducible promoter to which said transcriptional regulator binds are in the same expression construct.

8. The host cell of claim 6 wherein the transcriptional regulator is selected from the group consisting of: AraC, PrpR, RhaR, and XylR.

9. The host cell of claim 2 wherein at least one gene product is selected from the group consisting of: (a) an immunoglobulin heavy chain; (b) an immunoglobulin light chain; and (c) a fragment of any of (a)-(b).

10. The host cell of claim 2 wherein at least one gene product is a polypeptide that lacks a signal peptide and that forms at least three disulfide bonds.

11. The host cell of claim 2 wherein the host cell has an alteration of gene function of at least one gene encoding a transporter protein for an inducer of at least one said inducible promoter.

12. The host cell of claim 11 wherein the gene encoding a transporter protein is selected from the group consisting of araE, araF, araG, araH, rhaT, xylF, xylG, and xylH.

13. The host cell of claim 2 wherein the host cell comprises at least one expression construct encoding at least one disulfide bond isomerase protein.

14. The host cell of claim 13 wherein at least one expression construct encodes the disulfide bond isomerase protein DsbC.

15. The host cell of claim 2 wherein the host cell comprises at least one polynucleotide encoding a form of DsbC lacking a signal peptide.

16. The host cell of claim 2 wherein the host cell comprises at least one polynucleotide encoding Erv1p.

17. A method of producing a gene product, the method comprising growing a culture of the host cell of claim 2 and adding an inducer of at least one inducible promoter to the culture.

18. A kit comprising the host cell of claim 2 .

19. An Escherichia coli host cell comprising two or more types of expression constructs,

wherein the expression construct of each type comprises an inducible promoter and a polynucleotide sequence encoding a gene product to be transcribed from the inducible promoter; and

at least one of said inducible promoters is responsive to an inducer that is different than the inducer of another of said inducible promoters; and

each inducible promoter is selected from the group consisting of: an L-arabinose-inducible promoter, a propionate-inducible promoter, a rhamnose-inducible promoter, and a D-xylose-inducible promoter; and

wherein the host cell has a reduced level of gene function of at least one gene encoding a protein that metabolizes an inducer of at least one said inducible promoter; and

at least one of said gene products forms a multimer with another of said gene products; and

at least one gene product is selected from the group consisting of: (a) an immunoglobulin heavy chain; (b) an immunoglobulin light chain; and (c) a fragment of any of (a)-(b).

20. The host cell of claim 2 wherein the gene encoding a protein that metabolizes an inducer of at least one said inducible promoter is selected from the group consisting of araA, araB, prpB, prpD, rhaA, rhaB, rhaD, xylA, and xylB.

21. The host cell of claim 2 wherein the gene that encodes a reductase is trxB.

22. The host cell of claim 2 wherein the host cell has an altered gene function of a gene selected from the group consisting of gor and gshB.

23. The host cell of claim 2 wherein the host cell expresses a mutant form of AhpC.

24. The host cell of claim 2 wherein the host cell has a reduced level of gene function of at least one gene encoding a protein involved in biosynthesis of an inducer of at least one said inducible promoter.

25. The host cell of claim 24 wherein the gene encoding a protein involved in biosynthesis of an inducer of at least one said inducible promoter is selected from the group consisting of scpA/sbm, argK/ygfD, scpB/ygfG, scpC/ygfH, rmlA, rmlB, rmlC, and rmlD.

26. The host cell of claim 24 wherein the host cell comprises a deletion within the sbm-ygfDGH (scpA-argK-scpBC) operon.

27. The host cell of claim 12 wherein the gene encoding a transporter protein is araE, and the alteration of gene function of said araE gene is changing the promoter controlling expression of the host cell's chromosomal araE gene from an arabinose-inducible promoter to a constitutive promoter.

28. The host cell of claim 27 wherein the host cell has a reduced level of gene function of at least one gene selected from the group consisting of araA and araB; and wherein at least one expression construct comprises at least one arabinose-inducible promoter and a polynucleotide sequence encoding AraC.

29. The host cell of claim 27 wherein the host cell has a reduced level of gene function of at least one gene selected from the group consisting of prpB and prpD; and wherein at least one expression construct comprises at least one propionate-inducible promoter and a polynucleotide sequence encoding PrpR.

30. The host cell of claim 13 wherein at least one expression construct encodes the disulfide bond isomerase protein PDI.