title: Identification of an outer membrane protein of Escherichia coli, with a role in the coordination of deoxyribonucleic acid replication and cell elongation.
abstract: Protein G of molecular weight 15,000 is the fourth commonest protein in the outer membrane of Escherichia coli B/r. From experiments described here on the relationship of protein G production to cell elongation and septation, the hypothesis is proposed that protein G is a structural protein of cell elongation. Furthermore, a surplus of protein G is produced when deoxyribonucleic acid synthesis is arrested and septation is thereby prevented. Thus protein G may be an important coordination protein in E. coli for integration of deoxyribonucleic acid synthesis, cell envelope elongation, and septation. Inhibition of normal cell elongation in a rod configuration in E. coli B/r by the novel amidinopenicillanic acid FL1060 was accompanied by changes in the rate of appearance of protein G  and several other outer membrane proteins. The rate of appearance of protein G decreased some 70% within 60 min, in parallel with termination of rounds of normal cell elongation. Filament-inducing concentrations of nalidixic acid increased dramatically the rate of appearance of protein G. After 30 min a plateau level some 250% higher than the control value was reached. Similar kinetics were observed in parallel with filament formation induced by incubation of a dnaB mutant of E. coli at the nonpermissive temperature. No change in the rate of appearance of protein G was observed during cephalexin- or benzylpenicillin-induced filament formation, indicating that increased protein G production was not a secondary consequence of filamentation. Cells treated with FL1060 lost their ability to be induced for protein G formation, with nalidixic acid, in parallel with their loss of ability to initiate rounds of normal cell elongation. A pulse-chase experiment demonstrated that the protein G appearing in the outer membrane as a consequence of inhibition of deoxyribonucleic acid synthesis was the result of de novo synthesis rather than of interconversion from previously synthesized protein species. A preliminary characterization of protein G revealed several similarities with the well-characterized lipoprotein of the outer membrane of E. coli. A comparison of the incorporation of several 14C-labeled amino acids into protein G and the lipoprotein revealed substantial differences, however, perhaps ruling out a simple relationship between these two proteins.
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000096:biosynthesis; D002473:Cell Wall / Q000032:analysis / Q000378:metabolism; D002506:Cephalexin / Q000494:pharmacology; D004261:DNA Replication; D004269:DNA, Bacterial / Q000096:biosynthesis; D004926:Escherichia coli / Q000032:analysis* / Q000254:growth & development / Q000378:metabolism; D008970:Molecular Weight; D009268:Nalidixic Acid / Q000494:pharmacology; D010397:Penicillanic Acid / Q000494:pharmacology; D010400:Penicillin G / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D009268:Nalidixic Acid; D010397:Penicillanic Acid; D002506:Cephalexin; D010400:Penicillin G