COMBINED EFFECTS OF THE SIGNAL SEQUENCE AND THE MAJOR CHAPERONE PROTEINS ON THE EXPORT OF HUMAN CYTOKINES IN ESCHERICHIA-COLI

We have studied the export of two human proteins in the course of thei r production in Escherichia coli, The coding sequences of the granuloc yte macrophage colony-stimulating factor and of interleukin 13 were fu sed to those of two synthetic signal sequences to direct the human pro teins to the bacterial periplasm, We found that the total amount of pr otein varies with the signal peptide-cytokine combination, as does the fraction of it that is soluble in a periplasmic extract. The possibil ity that the major chaperone proteins such as SecB and the GroEL-GroES and DnaK-DnaJ pairs are limiting factors for the export was tested by overexpressing one or the other of these chaperones concomitantly wit h the heterologous protein, The GroEL-GroES chaperone pair had no effe ct on protein production. Overproduction of SecB or DnaK plus DnaJ res ulted in a marked increase of the quantity of human proteins in the pe riplasmic fraction, but this increase depends on the signal peptide-he terologous protein-chaperone association involved.