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Biosynthesis in vitro of tryptophanase by polyribosomes from induced cultures of Escherichia coli.

ABSTRACT: 1. Polyribosomes were isolated from Escherichia coli grown in media in which tryptophanase is induced and in which it is repressed. The polyribosomes from the induced bacteria had a small amount of tryptophanase activity associated with them. 2. A portion of the enzyme activity remained bound to polyribosomes during centrifuging in sucrose gradients. 3. Incubation of tryptophanase-containing polyribosomes with puromycin released enzyme activity. 4. The binding of the enzyme to the polyribosomes did not depend on the presence of DNA. 5. When the polyribosomes were incubated under conditions of protein synthesis with supernatant fraction obtained from repressed bacteria, a small but statistically significant increase in enzyme activity was produced. 6. When a radioactive amino acid was included in the incubation mixture for the tryptophanase system a radioactive protein was obtained whose chromatographic, electrophoretic and sedimentation properties were identical with those of tryptophanase. 7. The amount of incorporation was consistent with the amount of new enzyme synthesis predicted by the increase in enzyme activity. Both radioactive incorporation and increase in enzyme activity were shown to be energy-dependent and also negative controls were obtained by using zero-time incubations or polyribosomes isolated from either repressed cells or a mutant lacking the ability to produce tryptophanase. 8. The distribution of radioactive leucine in the carboxyl region of the newly labelled tryptophanase was examined by digesting the labelled protein with carboxypeptidases. It was shown that the radioactivity was more highly concentrated towards the carboxyl terminus when the incubation times for protein synthesis were shorter (implying that, with longer incubation times, longer lengths of polypeptide chain contained radioactive amino acid residues).

SUBMITTER: Bashar SA

PROVIDER: S-EPMC1176966 | biostudies-other | 1971 Jul

REPOSITORIES: biostudies-other

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Project description:BackgroundA fundamental characteristic of cells is the ability to divide. To date, most parameters of bacterial cultures, including cell division, have been measured as cell population averages, assuming that all bacteria divide at a uniform rate.ResultsWe monitored the division of individual cells in Escherichia coli cultures during different growth phases. Our experiments are based on the dilution of green fluorescent protein (GFP) upon cell division, monitored by flow cytometry. The results show that the vast majority of E. coli cells in exponentially growing cultures divided uniformly. In cultures that had been in stationary phase up to four days, no cell division was observed. However, upon dilution of stationary phase culture into fresh medium, two subpopulations of cells emerged: one that started dividing and another that did not. These populations were detectable by GFP dilution and displayed different side scatter parameters in flow cytometry. Further analysis showed that bacteria in the non-growing subpopulation were not dead, neither was the difference in growth capacity reducible to differences in stationary phase-specific gene expression since we observed uniform expression of several stress-related promoters. The presence of non-growing persisters, temporarily dormant bacteria that are tolerant to antibiotics, has previously been described within growing bacterial populations. Using the GFP dilution method combined with cell sorting, we showed that ampicillin lyses growing bacteria while non-growing bacteria retain viability and that some of them restart growth after the ampicillin is removed. Thus, our method enables persisters to be monitored even in liquid cultures of wild type strains in which persister formation has low frequency.ConclusionIn principle, the approaches developed here could be used to detect differences in cell division in response to different environmental conditions and in cultures of unicellular organisms other than E. coli.

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Biosynthesis in vitro of tryptophanase by polyribosomes from induced cultures of Escherichia coli.

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