Effects of Bacillus thuringiensis var. israelensis 20-kDa protein on production of the Bti 130-kDa crystal protein in Escherichia coli.

A 20-kDa protein of Bacillus thuringiensis var. israelensis (Bti) has been shown to be necessary for the efficient expression of the 27-kDa mosquitocidal protein gene in Escherichia coli. We have investigated the effects of this 20-kDa protein on the expression of two 130-kDa mosquitocidal protein genes (cryIVA, cryIVB) in E. coli by supplying the 20-kDa protein gene in trans. When a recombinant plasmid, pLH4BX, which was constructed to express cryIVA under the E. coli lac promoter on pUC19, coexisted with the 20-kDa protein gene, a striking increase in production of the fused CryIVA was detected. This was not accompanied by an increase in the amount of intracellular mRNA, suggesting that 20-kDa protein exerts a posttranscriptional effect. We conclude that the 20-kDa protein also stimulates the production of 130-kDa protein in E. coli.