Membrane protein alterations during the early stages of sporulation of Bacillus subtilis.

Abstract

AbstractMembrane protein alterations during the early stages of sporuloation were examined by polyacrylamide gel electrophoresis. Solubilized samples of the vegetative cell membrane (VCM), sporulation membrane fraction (SMF), and inner forespore membranes (IFM) were compared with respect to their protein compositions. The VCM contained 39 protein components, distinguishable as separate bands on gel electrophoresis, and these ranged in molecular weight from 16,000 to greater than 100,000. During the first 5 hr of sporulation, 6 of these 39 protein bands disappeared, 8 increased and 12 decreased in concentration, and 13 showed no discernible change. In addition, 15 new protein components were identified in the SMF during the fireist 5 hr. The new components consisted of 7 protein bands that were transiently associated with the SMF, and 8 proteins that persisted in the SMF from their time of appearance until at least T5 of sporulation. Comparison of the protein composition of the IFM with those of the VCM and SMF revealed that membrane protein alterations occur during sporulation.The turnover of H3‐tryptophan‐labeleld membrane protein was followed during growth and sporulation. During the 30 min of growth following a simple chase with excess unlabeled tryptophan, membrane protein appeared stable, whereas 5–10% of the nonmembrane protein turned over to acid‐soluble material. However, manipulation of the cells by dilution ito fresh medium, or centrifugation, as part of the chase procedure, resulted in elution of membrane protein to the cytoplasm. In contrast, proteins labeled during vegetative growth were always eluted to the cytoplasm during the first 2 hr of sporulation, and this was followed by a period of reassociation with the membrane fraction. The results are discussed with respect to membrane differentiation as it relates to spore development.