Release of a chimeric protein into the medium from Escherichia coli using the C‐terminal secretion signal of haemolysin

Recently, we have identified a novel topogenic sequence at the C terminus of Escherichia coli haemolysin (HlyA) which is essential for its efficient secretion into the medium. This discovery has introduced the possibility of using this secretion system for the release of chimeric proteins from E. coli directly into the medium. We have now successfully fused this C‐terminal signal to a hybrid protein containing a few residues of beta‐galactosidase and the majority of the E. coli outer membrane porin OmpF lacking its own N‐terminal signal sequence. We find that this chimeric protein is specifically translocated across the inner and outer membranes and is released into the medium. In addition, we have further localized the HlyA secretion signal to the final 113 amino acids of the C terminus. In fact, a specific secretion signal appears to reside at least in part within the last 27 amino acids of HlyA.