title: Inhibition of Escherichia coli division by protein X.
abstract: We propose that protein X provides the connection between damage to Escherichia coli DNA and inhibition of septation and cell division. This connection is needed to guarantee that each new bacterium receives a complete DNA copy. We present several new experiments here which demonstrate that the degree to which septation is inhibited following damage to DNA is correlated with the amount of protein X that is produced. Rifampin selectively blocks protein X production. This drug was shown to allow cells whose DNA had been damaged by nalidixic acid to resume septation. Several mutants formed septa-less filaments and also produced protein X at 42 degrees C; rifampin both inhibited their production of protein X and permitted them to form septa and divide. Essentially complementary results were obtained with a dnaA mutant which at 42 degrees C stopped making DNA, did not produce protein X, and continued to divide; added bleomycin degraded DNA, induced protein X, and inhibited septation. These results, as well as previous observations, are all consistent with the proposal that protein X is produced as a consequence of DNA damage and is an inhibitor of septation. We suggest that septation could require binding of a single-stranded region of DNA to a septum site in the membrane. Protein X could block this binding by combining with the DNA. This control could provide an emergency mechanism in addition to the usually proposed coordination in which completion of DNA synthesis creates a positive effector for a terminal step of septation. Or it could be the sole coordinating mechanism, even under unperturbed growth conditions.
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000502:physiology*; D001761:Bleomycin / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D004269:DNA, Bacterial / Q000096:biosynthesis / Q000378:metabolism*; D004926:Escherichia coli / Q000166:cytology*; D008954:Models, Biological; D009268:Nalidixic Acid / Q000494:pharmacology; D012293:Rifampin / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D001761:Bleomycin; D009268:Nalidixic Acid; D012293:Rifampin