Expression and purification of thioredoxin fusion proteins.

This unit describes a gene fusion expression system that uses thioredoxin, the product of the Escherichia coli trxA gene, as the fusion partner. The inherent thermal stability of thioredoxin and its susceptibility to quantitative release from the E. coli cytoplasm by osmotic shock can also be exploited as useful tools for thioredoxin fusion protein purification. In this protocol, a fusion of trxA to any desired gene is constructed and the resulting fusion protein is expressed in an appropriate host strain. Additional protocols describe E. coli cell lysis and fractionation, osmotic release of thioredoxin fusion proteins from the E. coli cytoplasm, and heat treatment to purify some thioredoxin fusion proteins.