The delta-endotoxin proteins accumulate in Escherichia coli as a protein-DNA complex that can be dissociated by hydrophobic interaction chromatography

The insecticidal protein CryIAc accumulated to form inclusion bodies in Esc herichia coli upon overexpression of the cloned gene. The solubilized inclu sion bodies contained the delta-endotoxin in association with DNA fragments of about 25 kb. The protein-DNA complex could be dissociated and the delta -endotoxin purified by hydrophobic interaction chromatography on phenyl-Sep harose. The DNA was washed out in the high-salt buffer while the delta-endo toxin was bound to the matrix and was eluted at 4 degrees C by a stepwise d ecreasing potassium chloride gradient. The DNA-protein complex also contain ed plasmids harbored by the host strain. The plasmid DNA associated with th e complex became competent to transform E. coli only after it was dissociat ed from the delta-endotoxin. The hydrophobic interaction chromatography pro vides an efficient method for the purification of DNA-free activated toxin, (C) Academic Press.