REGULATION OF INSECTICIDAL CRYSTAL PROTEIN-PRODUCTION IN BACILLUS-THURINGIENSIS

The production of insecticidal crystal proteins (ICPs) in Bacillus thu ringiensis normally coincides with sporulation, resulting in the appea rance of parasporal crystalline inclusions within the mother cell. In most instances, the temporal and spatial regulation of ICP gene expres sion is determined at the transcriptional level by mother-cell-specifi c sigma factors that share homology with sigma(E) and sigma(K) from Ba cillus subtilis. The cryIII ICP genes are a notable exception; these g enes are transcribed from sigma(A)-like promoters during vegetative gr owth, are induced or derepressed at the onset of stationary phase, and are overexpressed in sporulation mutants of B. thuringiensis blocked in the phosphorylation of SpoOA, a key regulator of sporulation initia tion. Transcription alone, however, cannot account for the impressive ability of this bacterium to accumulate insecticidal proteins. A varie ty of post-transcriptional and post-translational mechanisms also cont ribute to the efficient production of ICPs in B. thuringiensis, thus m aking this bacterium a cost-effective biological control agent.