Eukaryotic signal sequence transports insulin antigen in Escherichia coli

We made a series of plasmids with unique Pst restriction sites within or near the DNA that encodes the penicillinase signal sequence. Inserted DNA can be read in all three frames both within and immediately after the signal sequence. We cloned Pst-terminated DNA copies of the structural information for rat proinsulin and preproinsulin into these plasmids, forming a large number of hybrid penicillinase (bacterial) and insulin (eukaryotic) signal sequences. We then compared the levels of insulin antigen in the Escherichia coli periplasm with those inside the cells. We conclude that either the bacterial or the eukaryotic signal is sufficient to transport rat insulin antigen into the periplasmic space.