The CryIVD protein is involved in the overall toxicity of the Bacillus thuringiensis subsp. israelensis parasporal inclusions and is one of the four major components of the crystals. Determination of the DNA sequence indicated that the cryIVD gene is the second gene of an operon which includes three genes. The first one encodes a 19-kDa polypeptide and has sequence homology with the orf1 gene of the Bacillus thuringiensis cryIIA and cryIIC operons. The second and third genes have already been identified and encode the CryIVD crystal protein and the P20 polypeptide, respectively. The promoter region was located by deletion analysis, and the 5' end of the mRNA was determined by primer extension mapping. Transcription of the cryIVD gene in B. thuringiensis subsp. israelensis strains is induced 9 h after the beginning of sporulation. Sequence analysis indicated two potential promoters, a strong one and a weak one, recognized respectively by the RNA polymerase associated with the sigma 35 or the sigma 28 factor of B. thuringiensis (sigma E and sigma K of Bacillus subtilis, respectively). Transcriptional lacZ fusion integrated in single copy into the chromosome of various B. subtilis sporulation mutants confirmed the sigma E dependence of cryIVD gene transcription.