Study On The Codon Usage Of Chinese Hamster Ovary Cells

The Chinese hasmster ovary(CHO) cells is one of the most important system for expression of foreign gene, but the expression level is low.Considerable efforts to increase the production in CHO cells have been concentrated in optimizing the expression vector with the effective promoters and enhancers.Another way to increase the protein yield is to modify the coding sequence of an individual gene without altering the amino acid sequence .This stategy has been used sucessfully in E.coli and S.cervisiae.Similar studies have not yet been extensively exercised in mammalian systems.Here, we investigate the codon usage of Chinese hasmster ovary cells in order to increase the production of foreign gene in CHO cells..CHO cells defected with Dihydroflate reductase (CHO CHO dhfr ) is most widely used in expression of foreign gene,which is induced from immortal cell lines.Because the number of cDNA from CHO dhfr~- cells in GenBank is still limited,so it is nessary to construct a cDNA library of CHO dhfr- cells to get more cDNA .High-abudence mRNA derived from CHO dhfr- cells was isolated ,cDNA was synthesized and ligated to EcoRI-digested plasmid of pUC18 for subsequent introduction into E.coli.Because Codon bias is independent of gene length up to 100 codons,150 clones are selected randomly and each clone was sequenced with more than 550bp. A dataset of 50 protein-coding sequences was yield through discarding tRNA gene, rRNA gene,pseudogene,repeat region,non-coding sequence and duplicate sequencesOpen reading frames(ORF) of 50 coding sequences are predicted using BLAST program. Percentage frequencies of the synonymous codons each amino acid of CHO 中 ProCHO dhfr- cells are caculated by DNASIS soft ware ,and compared with those of Chinese hamster in the database GUTG (codon usage tabulated from GenBank). The optimal codons for most amino acids are identical between Chinese...