Patent ID: 8653249

Claim:
An expression vector for producing a foreign gene-derived protein in a mammalian host cell, which comprises: (a) a translation-impaired drug resistance gene cassette comprising a region with rare codons wherein the rare codons comprise GCA for alanine, CGA for arginine, AAU for asparagine, GAU for aspartic acid, UGU for cysteine, CAA for glutamine, GAA for glutamic acid, GGU for glycine, CAU for histidine, UUA for leucine, AAA for lysine, CCA for proline, UUU for phenylalanine, UCA for serine, ACU for threonine, UAU for tyrosine, and GUA for valine, wherein from the 5′ end of the drug resistance gene, each of at least the first 30% of the drug resistance gene codons is replaced by the rare codon encoding the same amino acid as the drug resistance gene codon, wherein the translation-impaired drug resistance gene cassette uses a promoter whose enhancer portion has been removed, and wherein the drug resistance gene is a neomycin phosphotransferase gene (NTP gene); and (b) a gene cassette comprising a cloning site for integration of a foreign gene between a transcriptionally active promoter and a stable polyadenylation signal.