ABSTRACT
Growth factor-toxin fusion proteins may also be used to regulate immune responses by eliminating subsets of lymphocytes or mononuclear cells that express specific cytokine receptors. A variety of genetic constructions employing several types of microbial-expression plasmids have been used successfully to produce growth factor-toxin fusion proteins. In particular, the optimal transcriptional promoters, ribosome-binding sites, and distances between the promoter and translational start site for each genetic construct are often different for different growth factor-toxin fusion proteins. The major obstacle to bringing several growth factor-toxin fusion proteins to clinical trials is the production and purification of sufficient quantities of biologically active protein. One of the most critical requirements for successful large-scale isolation of a recombinant fusion protein from bacteria is proper formation of disulfide bonds. An appropriate refolding step is generally essential for recovery of biologically active foreign proteins from bacteria.
