The proHNP1 cDNA sequence encoding the natural 75 amino acid residue sequence extended by 5 amino acids (DDDDK; enterokinase recognition site) at the N-terminus was amplified using oligonucleotides (59-GCGAATTCGATGACGATGACAAGGAGCCACTCCAGG-CAAGAGCTG) and (59-GCGGATCCGGTACCTCGAGTCAG-CAGCAGAATGCCCAGAGTC) with plasmid PEC2081 (proHNP1 cloned in pCR2.1 Topo vector) as template. EcoRIand XhoI-digested DNA was ligated into pET28a+ vector to generate plasmid PEC2129 which encodes proHNP1 with a 41 amino acid residue N-terminal sequence containing the His 6 -tag (His 6 -proHNP1; Fig. 1 ). The plasmid was used to transform Escherichia coli BL21(DE3)(codon+), generating strain PEC2132-1 which was used for expression and purification of His 6 -proHNP1.