A chloroplast envelope-transfer sequence functions as an export signal in Escherichia coli

The small subunit precursor of pea ribulose-1,5-bisphosphate carboxylase/oxygenase engineered with prokaryotic elements was expressed in Escherichia coli. This resulted in a dependable level of synthesis of the precursor protein in E. coli. The bacterially synthesised plant precursor protein was translocated from the cytoplasm and targeted to the outer membrane of the envelope zone. During the translocation step, a significant proportion of the precursor was processed to a soluble, mature SSU and found localised in the periplasm. The determined amino acid sequence of the isolated precursor showed that it had a deletion of an arginine residue at position -15 in the transit peptide. Expression of this transit peptide-appended mammalian cytochrome b(5) in E. coli displayed a targeting profile of the chromogenic chimera that was similar to that observed with the plant precursor protein.