Galactose-Binding Protein by the Cell Cycle of Escherichia coli

The synthesis of the periplasmic galactose-binding protein of E. coli is regulated by events occurring during its cell cycle, and proceeds in synchronized cells for only a short period after cell division is completed. Transport activity mediated by the fl-methylgalactoside transport system follows closely the synthesis pattern of the binding protein. A mutant, E. coli BUG-6, exhibits temperature-sensitive cell division [Reeve et al. (1970) J. Bacteriol. 104, 1052-10641, synthesizing galactose-binding protein at the permissive but not at the nonpermissive temperature. Galactosebinding protein synthesized at the permissive temperature is not degraded after the culture is shifted to the nonpermissive temperature. Polyacrylamide gel electrophoresis of the periplasmic proteins of BUG-6 grown at the permissive and nonpermissive temperatures suggests that several, but not all, periplasmic proteins are subject to the same regulatory control by the cell cycle as the galactose-binding protein. We have been studying a bacterial sugar transport system in Escherichia coli, the P-methylgalactoside transport system, in particular the function of the periplasmic galactose-binding protein (1) in this transport system. Several biochemical (2) and genetic (3) lines of evidence strongly indicate the essential function of this protein in the transport mechanism. Studies by Lengeler, Herman, and Uns6ld (unpublished) on this transport system show that the specific transport activity (active transport of galactose) exhibits large fluctuations during logarithmic growth of the bacterial culture. With a sensitive test for the galactose-binding protein, an essential component of the transport system, we are now able to show that transport activity of the fl-methylgalactoside transport system and synthesis of the galactose-binding protein is regulated by the cell cycle of E. coli. METHODS AND MATERIALS Bacterial Strains. W3092cy(F-, lacY, galK) has been described (6). BUG-6 and its parent M-2 were isolated by Reeve et al. (7-9) and were kindly provided by them. Both strains are prototrophs but appear to be negative in lac and gal. Both are endogenously induced for #-methylgalactoside transport activity and galactose-binding protein synthesis. BUG-6 (lac+) was constructed by P1 transduction (10), with lysates grown on K12 3000 and selection on minimal lactose plates. BUG-6 (phoR) was constructed by P1 transduction (10), with lysates grown on strain C2 (11) and selection on minimal plates containing f8-glycerol-phosphate as carbon source. Enzymatic Activities. fl-Galactosidase was assayed in toluenized cells according to Novick and Weiner (12). Alkaline phosphatase was assayed in whole cells according to Brockman and Heppel (13). The activity of lactose uptake was measured according to Winkler and Wilson (14) with the modification that room temperature was used for the incubation mixture as well as the washings. Proline uptake was measured in the same way as described for galactose in the legend to Fig. 1. '4C-Labeled compounds were obtained from New England Nuclear in the highest available specific radioactivity.