Changes of Membrane Proteins and Their Relation to Deoxyribonucleic Acid Synthesis and Cell Division of Escherichia coli

Abstract

Abstract Escherichia coli K-12 were treated in five ways to alter DNA synthesis, cell division, or both. Their membranes were then examined for changes. The bacteria were grown in the presence of radioactive l-arginine to label the membranes. 14C-Arginine was used for the experimental culture and 3H-arginine for the control, or vice versa. The cells were mixed, and their membranes were isolated and run on acrylamide gels in 0.5% sodium dodecyl sulfate to obtain a spectrum of proteins. Gel fractions were counted for both labels in order to find differences caused by the experimental treatment. Two principal changes were found in the membranes. At a position Y, corresponding to molecular weight 34,000, less protein appeared whenever DNA synthesis was inhibited. At a position X, molecular weight 39,000, extra protein appeared whenever bacterial division was inhibited. Rates of changes of Y and X were examined during thymidine deprivation to stop DNA synthesis, and after restoration of thymidine. Whereas DNA synthesis was rapidly affected, the changes of Y were gradual, suggesting that Y is not responsible for the synthesis of DNA; rather, its slowed rate of formation might be a consequence of arrested DNA synthesis. Changes of X were more immediate, and could possibly be responsible for altered cell division which is only affected after a lag. No significant changes in synthesis of X and Y were noted between cells near the beginning and end of the division cycle, suggesting that these proteins are normally made continuously or are not produced under normal conditions. Pulse chase experiments indicated that X and Y do not have a precursor-product relation. This is also suggested by the kinetic studies. Temperature-sensitive changes of membrane proteins in a previously described temperature-sensitive DNA synthesis mutant were further examined. The mutation appears to influence the formation of Y indirectly by stopping DNA synthesis. But production of X in the absence of DNA synthesis was much less in the mutant than in the wild type, which is compatible with ability of the mutant to divide even in the absence of DNA synthesis.