Retention of antigenicity by a fragment of Aeromonas salmonicida 70-kDa serine protease which includes the primary substrate binding site expressed as β-galactosidase hybrid proteins

Abstract. A 587 bp 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 DH5α, produced a 142-kDa hybrid protein in high yield. The hybrid consisted of a fusion between an essentially complete β-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 α-galactosidase subunit. Both fusion proteins were shown to possess recognizable epitopes by dot blotting against rabbit anti- A. salmonicida 70-kDa serine protease antibody.