EFFECT OF A 20-KILODALTON PROTEIN FROM BACILLUS-THURINGIENSIS SUBSP ISRAELENSIS ON PRODUCTION OF THE CYTA PROTEIN BY ESCHERICHIA-COLI

CytA, a 27-kDa cytolytic crystal protein of Bacillus thuringiensis subsp. israelensis, is produced only at very low levels by recombinant Escherichia coli cells unless a 20-kDa B. thuringiensis subsp. israelensis protein is also present (K.M. McLean and H.R. Whiteley, J. Bacteriol. 169:1017-1023, 1987; L.F. Adams, J.E. Visick, and H.R. Whiteley, J. Bacteriol. 171:521-530, 1989). However, the data reported here demonstrate that the 20-kDa protein is not required for high-level CytA production in E. coli strains carrying mutations in rpoH, groEL, or dnaK, all of which affect the proteolytic ability of the cells. The 20-kDa protein also increase the amount of CryIVD (another B. thuringiensis subsp. israelensis crystal protein) and LacZX90 (a mutant of beta-galactosidase) made by E. coli. The latter phenomenon is attributable to an increase in the half-life of LacZX90, suggesting that the 20-kDa protein may stabilize this protein. The effect of the 20-kDa protein was also examined in vitro and in a T7 RNA polymerase expression system, and the possible significance of these results for the timing of proteolysis and of 20-kDa protein from E. coli extracts provides evidence for a protein-protein interaction that may be related to the mechanism of action of the 20-kDa protein.