Protein turnover and the formation of protein inclusions during sporulation of Bacillus thuringiensis

Abstract

Studies have centred around the formation of protein, crystalline, parasporal inclusions and general protein metabolism in cells of Bacillus thuringiensis during sporulation in a nutrient-free medium. Analysis of the metabolic pool shows that insufficient free amino acids to account for synthesis of all the crystal protein are present at the time of transfer to the nutrient-free medium. C14-labelled amino acids, added either during growth or sporulation, are incorporated into the crystals. [C14] glutamic acid, whether it is added during growth or sporulation, is incorporated into the same positions in the polypeptide chains of the crystal protein. When cells are prelabelled with [C14] phenylalanine, the addition of unlabelled phenylalanine to the sporulation medium prevents incorporation of label into the crystals. It is concluded that the crystal protein is synthesized from amino acids during sporulation and that, under the conditions employed, these amino acids are derived largely from the breakdown of vegetative-cell proteins. Further studies show that there is a high percentage of intracellular protein turnover during sporulation, and that other proteins, in addition to the crystal protein, are synthesized.