BIOCHEMICAL-CHARACTERIZATION OF BACILLUS-THURINGIENSIS CYTOLYTIC DELTA-ENDOTOXINS

The entomocidal delta-endotoxins CytA and CytB produced by Bacillus th uringiensis (Bt) subspecies israelensis and kyushuensis respectively s howed a similar level of toxicity to mosquito larvae but were not toxi c to the larvae of the lepidopteran Manduca sexta. CytA and CytB are a lso similar in sequence, predicted secondary structure and alpha-helic al content, the only obvious difference being a C-terminal fifteen res idue 'tail' on CytB. Investigations of the function, if any, of the Cy tB C-terminal 'tail' showed that this delta-endotoxin is highly expres sed and forms inclusions in an acrystalliferous Bt mutant without the aid of the 20 kDa 'helper' protein from Bt subspecies israelensis whic h is essential for CytA inclusion formation. After proteinase K treatm ent, CytA and CytB were processed to virtually the same points in a se quence alignment and were equally haemolytic in vitro. However, the re sults suggested that unprocessed CytB differs from unprocessed CytA in that the former is not haemolytic.