[The changes of rare codons increase expression level of SEA].

The rare codons of a fragment in staphylococcal enterotoxin A gene were turned into the most high usage frequency codons in E. coli by overlap PCR technique. Genes of sea and seam were cloned into 7ZTS expression vector and transformed into JM109(DE3), respectively. The result shows that expression level of sea gene was very low, but the expression level of seam was as high as 15% of total cell proteins. The expression product shows activity of antitumor in vivo.