Methods of expressing products in mammalian cells

1. A method of expressing a product in a mammalian cell, the method comprising:

(a) contacting mammalian cells lacking expression of a protein with (i) an exogenous mammalian nucleic acid comprising a nucleic acid encoding said protein and with (ii) an expressible nucleic acid encoding said product, wherein said contacting results in uptake of said exogenous mammalian nucleic acid into at least one of said cells,

wherein the protein is selected from the group consisting of: argininosuccinate lyase, cystathionine G-lyase, cystathionine b-synthase, glycine N-methyltransferase, pyrroline-5-carboxylate synthetase, phenylalanine 4-monooxygenase, carbamoyl-phosphate synthase (ammonia), ornithine carbamoyltransferase (mitochondrial), ornithine transaminase (mitochondrial), methionine adenosyltransferase, adenosylhomocysteinase, propionyl-CoA carboxylase (mitochondrial), methylmalonyl-CoA epimerase (mitochondrial), methylmalonyl-CoA mutase, myo-Inositol-1-phosphate synthase, thymidylate synthase, nucleoside-diphosphatase (dUDP), carbonate anhydrase, adenosine kinase, sarcosine oxidase, alphaketobutyrate dehydrogenase (mitochondrial), phosphatidylserine decarboxylase, glucose-6-phosphate isomerase, myo-inositol 1-phosphatase, ribonucleoside-diphosphate reductase, and dihydropteridine reductase;

(b) placing said mammalian cells in a selection medium, wherein the components of the selection medium exclude a component that complements the lack of expression of said protein;

(c) culturing said mammalian cells in said selection medium, wherein the culturing of said mammalian cells selects for at least one mammalian cell that expresses from said exogenous mammalian nucleic acid the protein lacking expression in said mammalian cell; and

(d) culturing said selected mammalian cell under conditions for expression of said product.

2. The method of claim 1 , wherein the component of the selection medium is selected from the group consisting of: arginine, cysteine, proline, tyrosine, myo-inositol, thymidine, ethanolamine, glucose, asparagine and glutamine.

3. The method of claim 1 , further comprising isolating the product expressed in the selected mammalian cell.

4. The method of claim 1 , wherein the selected mammalian cell comprises a gene disruption of the protein.

5. The method of claim 4 , wherein the gene disruption is a gene knockout.

6. The method of claim 1 , wherein the protein is selected from the group consisting of: argininosuccinate lyase, cystathionine G-lyase, cystathionine b-synthase, glycine N-methyltransferase, pyrroline-5-carboxylate synthetase, and phenylalanine 4-monooxygenase.

7. The method of claim 1 , wherein the component of the selection medium is selected from the group consisting of arginine, cysteine, proline, and tyrosine.

8. The method of claim 1 , wherein the exogenous mammalian nucleic acid is a mammalian expression vector.

9. The method of claim 1 , wherein the cell is a Chinese Hamster Ovary (CHO) cell.

10. A method of expressing a product in a mammalian cell, the method comprising:

(a) culturing mammalian cells comprising an exogenous mammalian nucleic acid that comprises (i) a nucleic acid encoding a protein not expressed in the mammalian cells and (ii) an expressible nucleic acid encoding a product, in a selection medium, wherein the components of the selection medium exclude a component that complements the lack of expression of the protein,

wherein the protein is selected from the group consisting of: argininosuccinate lyase, cystathionine G-lyase, cystathionine b-synthase, glycine N-methyltransferase, pyrroline-5-carboxylate synthetase, phenylalanine 4-monooxygenase, carbamoyl-phosphate synthase (ammonia), ornithine carbamoyltransferase (mitochondrial), ornithine transaminase (mitochondrial), methionine adenosyltransferase, adenosylhomocysteinase, propionyl-CoA carboxylase (mitochondrial), methylmalonyl-CoA epimerase (mitochondrial), methylmalonyl-CoA mutase, myo-Inositol-1-phosphate synthase, thymidylate synthase, nucleoside-diphosphatase (dUDP), carbonate anhydrase, adenosine kinase, sarcosine oxidase, alphaketobutyrate dehydrogenase (mitochondrial), phosphatidylserine decarboxylase, glucose-6-phosphate isomerase, myo-inositol 1-phosphatase, ribonucleoside-diphosphate reductase, and dihydropteridine reductase;

(b) selecting mammalian cells from step (a) that express the exogenous mammalian nucleic acid thereby allowing growth of the mammalian cells in the selection medium; and

(b) culturing the selected mammalian cells under conditions for expression of the product.

11. The method of claim 10 , wherein the protein is selected from the group consisting of: argininosuccinate lyase, cystathionine G-lyase, cystathionine b-synthase, glycine N-methyltransferase, pyrroline-5-carboxylate synthetase, and phenylalanine 4-monooxygenase.

12. The method of claim 10 , wherein the component of the selection medium is selected from arginine, cysteine, proline, tyrosine, myo-inositol, thymidine, ethanolamine, glucose, asparagine and glutamine.

13. The method of claim 12 , wherein the component of the selection medium is selected from the group consisting of arginine, cysteine, proline, and tyrosine.

14. The method of claim 10 , further comprising isolating the product expressed in the selected mammalian cell.

15. The method of claim 10 , wherein the exogenous mammalian nucleic acid is a mammalian expression vector.

16. The method of claim 10 , wherein the cell is a Chinese Hamster Ovary (CHO) cell.