SDS-PAGE analysis of the insoluble fraction of a recombinant Escherichia coli cell extract revealed that the DNA fragment containing the coding region of the cryIA(a) gene (3528 bp) with 80-bp upstream and 153-bp downstream flanking regions, placed under the control of the tac promoter in pTTQ19, produces a considerable amount of CryIA(a) proteins in E, coli cells grown at 37 degrees C without IPTG induction. Under similar conditions, the presence of an additional upstream region (ca. 400 bp) of the cryIA(a) gene was found to increase the production of CryIA(a) proteins about 2-fold in E. coil. Overexpression of the cryLA(a) gene in E. coli without the addition of IPTG offers the advantage of reduced production costs.