Vectors for animal cells and use thereof
Protein synthesis inhibitor resistance genes (typified by a cycloheximide resistance gene) are capable of imparting resistance to a protein synthesis inhibitor (typified by cycloheximide) to animal cells sensitive to the inhibitor. The genes have a sequence mutated by substitution in a gene encoding a ribosome-constituting protein derived from an animal. The genes may be placed in recombinant vectors, including expression vectors containing the gene together with a foreign protein structural gene.
1. A process for selecting an animal cell strain resistant to a protein synthesis inhibitor, comprising:
introducing an expression vector containing (A) a protein synthesis inhibitor resistance gene which is capable of imparting cycloheximide resistance to animal cells sensitive to cycloheximide and which encodes the amino acid sequence comprising SEQ ID NO: 11 or a sequence at least 99% homologous thereto, wherein said amino acid sequence contains an amino acid other than proline at the position corresponding to position 54 of SEQ ID NO: 11 and (B) a gene encoding a foreign protein in an expressible state, into animal cells sensitive to cycloheximide,
culturing the cells with the protein synthesis inhibitor cycloheximide, to express the foreign protein, and
selecting the animal cell strain that is resistant to cycloheximide.
2. A process according to claim 1 , wherein the animal cell strain sensitive to cycloheximide is derived from a mammal.
3. A process according to claim 2 , wherein the animal cell is a CHO cell from the ovary of a Chinese hamster.
4. A process according to claim 3 , wherein the animal cell is a CHO cell lacking dihydrofolic acid reductase.
5. A process for producing a protein, characterized by culturing transformed animal cells containing the expression vector defined in claim 1 and collecting a foreign protein expressed by the cells.
6. A process according to claim 1 , wherein the sequence at least 99% homologous encodes a ribosome protein L44, which has the amino acid sequence comprising SEQ ID NO:12.