A non-covalent NH2-terminal pro-region aids the production of active aqualysin I (a thermophilic protease) without the COOH-terminal pro-sequence in Escherichia coli.

The precursor of aqualysin I, an extracellular protease produced by Thermus aquaticus, consists of four domains: an N-terminal signal peptide, an N-terminal pro-sequence, the protease domain and a C-terminal pro-sequence. In an Escherichia coli expression system, mature and active aqualysin I is formed by treatment at 65 degrees C and the N-pro-sequence is required for its production. Complete deletion of the C-pro-sequence did not affect the production of active aqualysin I, indicating that the C-pro-sequence is not essential. A non-covalent N-pro-region was separately synthesized from the protease domain with or without the C-pro-sequence. In this system, mature and active aqualysin I was detected only when the C-pro-sequence was deleted.