CytA protein, a delta-endotoxin of Bacillus thuringiensis subsp. israelensis is associated with DNA

CytA protein (27 kDa) is produced by Bacillus thuringiensis subsp. israelensis (BTI) and is contained in its inclusion bodies. We previously reported the isolation of 25 kDa portion of CytA protein (p25-CytA protein) and its strong cytotoxic activity to mammalian cells. When p25-CytA protein was applied to an anion-exchange column for further purification, three fractions (M1, M2 and M3) were separated. M1 and M2 fractions were both shown to be 25 kDa protein, while M3 was a high molecular weight complex composed of 25 kDa protein and DNA. Purification and amino acid sequence analysis showed that M1 and M2 fractions were proteins lacking 29 and 31 N-terminal amino acids from CytA protein, respectively, and M3 was M1 protein associated with DNA. DNA was detected in BTI cells co-localizing with inclusion bodies. Both M1 and M2 proteins could bind to double-stranded DNA of BTI genome in vitro; the DNA binding ability of M1 protein was higher than that of M2 protein. These results suggested that CytA protein has DNA binding ability and is associated with DNA in the mother cell.