The cloning and expression of the synthetic leu-enkephalin gene in E. coli

The synthetic leu-enkephalin (LEK) gene was joined with pBR322 and transformed to E. coli. The recombinant plasmids containing the LEK gene were selected by colony hybridization, and characterized by restriction mapping and Southern's technique. The lac operon was used to control the expression of the LEK gene. A recombinant plasmid, pEL 103, in which the lac operon and LEK gene are transcribed in the same direction, produces LEK in E. coli. The level of LEK detected by radioimmunoassay reaches 426 ng per mg of bacterial protein.