Increased expression in Escherichia coli of a synthetic gene encoding human somatomedin C after gene duplication and fusion.

A synthetic gene coding for human somatomedin C (SMC) was inserted into an Escherichia coli plasmid vector that contains the bacteriophage lambda pL promoter. Intracellular accumulation of the gene product after induction of the promoter was found to be low. A 200-fold greater yield was obtained with a similar plasmid containing two translationally fused copies of the SMC gene. A series of such tandem genes truncated at their 3' ends were generated with nuclease Bal 31. These gave intermediate expression levels that correlated with the expected sizes of their gene products. Comparison of RNAs extracted from cells containing either the monomer or tandem SMC gene constructions showed that there was no significant difference in expression at the transcriptional level. Pulse-chase experiments demonstrated that the tandem SMC protein was far more stable than the monomer SMC product.