RETENTION OF ANTIGENICITY BY A FRAGMENT OF AEROMONAS-SALMONICIDA 70-KDA SERINE PROTEASE WHICH INCLUDES THE PRIMARY SUBSTRATE BINDING-SITE EXPRESSED AS BETA-GALACTOSIDASE HYBRID PROTEINS

A 587bp Pvu II restriction fragment from the 70-kDa Aeromonas salmonicida serine protease gene, containing the 'active serine' site sequence of the enzyme, has been cloned into the Sma I restriction site of pUEX2 which on expression, in Escherichia coli DH5alpha, produced a 142-kDa hybrid protein in high yield. The hybrid consisted of a fusion between an essentially complete beta-galactosidase subunit and approximately one-third of the serine protease. A further 42-kDa hybrid was constructed from the same fragment of serine protease fused to a truncated beta-galactosidase subunit. Both fusion proteins were shown to possess recognizable epitopes by dot blotting against rabbit anti-A. salmonicida 70-kDa serine protease antibody.