Synchronous Cultures of Chlamydomonas reinhardti: Properties and Regulation of Repressible Phosphatases

De novo synthesis of phosphatase (derepression) in orthophosphate deprived synchronously growing Chlamydomonas reinhardti has been demonstrated by using a double labelling isotope technique coupled with cellulose acetate electrophoresis. Repressed and derepressed phosphatase exhibited different enzymatic properties as pH optimum, electrophoretic pattern, K_m and K_i values. Especially the acid phosphatase was located near the cell surface. Inorganic, cold TCA-extractable ³²P, decreased during the first 1–2 h after phosphate deprivation when there was little or no net synthesis of phosphatase. Results of experiments with additions of orthophosphate and cycloheximide to derepressed cells, indicated that the derepressible enzyme was relatively unstable, while its m-RNA was relatively stable.     

Enzyme Pattern and Aerobic Growth of Saccharomyces cerevisiae Under Various Degrees of Glucose Limitation

The enzyme pattern of Saccharomyces cerevisiae was followed during batch growth and in continuous culture in a synthetic medium limited for glucose under aerobic conditions. Seven enzymes were measured: succinate-cytochrome c oxidoreductase, malate dehydrogenase, nicotinamide adenine dinucleotide-linked glutamate dehydrogenase, malate synthase, isocitrate lyase, aldolase, and nicotinamide adenine dinucleotide phosphate (NADP(+))-linked glutamate dehydrogenase. During fermentation of glucose and high growth rate (mu) during the first log phase in batch experiments, the first five enzymes (group I) were repressed, and aldolase and NADP(+)-linked glutamate dehydrogenase (group II) were derepressed. During growth on the accumulated ethyl alcohol and lower mu, the group I enzymes were preferentially formed and the other two were repressed. A sequence of derepression of the group I enzymes was found during the shift from glucose to ethyl alcohol metabolism, which can be correlated with a strong increase in the percentage of single (nonbudding) cells in the population. A correlation between the state of cells in the budding cycle and enzyme repression and derepression is suggested. In continuous culture, the enzyme pattern was shown to be related to the growth rate. The group I enzymes were repressed at high growth rates, while the group II enzymes were derepressed. Each enzyme exhibits a different dependence. The enzyme pattern is shown to depend on the rate of substrate consumption as well as on the type of metabolism and to be correlated with the budding cycle. The enzyme pattern is considered to be controlled by changes of intracellular catabolic or metabolic conditions inherent in the division cycle.     

Isoleucine and Valine Metabolism of Escherichia coli XVI. Pattern of Multivalent Repression in Strain K-12

The levels of the five enzymes required for isoleucine and valine synthesis were examined under several growth conditions in strain K-12 of Escherichia coli and mutants derived from it. In strains with wild type repressibility, the same pattern of derepression was found on limiting isoleucine as is found to be constitutive in strain Tir-8, which has an altered isoleucine-activating enzyme. Homoserine dehydrogenase, which is essential for the biosynthesis of threonine and is normally derepressed on limiting isoleucine or threonine, is also derepressed in strain Tir-8. Threonine deaminase and homoserine dehydrogenase were partially repressed in strain Tir-8 by very high levels of isoleucine, but were not further derepressed over levels in minimal medium by limiting isoleucine.     

Initiation of chromosome replication in Escherichia coli. I. Requirements for RNA and protein synthesis at different growth rates

The effects of inhibition of protein and RNA synthesis on initiation of chromosome replication in Escherichia coli$\text{B}\text{r}$ were determined by measuring rates of DNA synthesis during the division cycle before and after addition of chloramphenicol and rifampicin. The ability of cells to initiate a round of replication depended upon the pattern of chromosome replication during the division cycle. Initiation in the presence of chloramphenicol (200 μ/ml) and rifampicin (100 gmg/ml) was observed only in slowly growing cells which normally initiated a new round between the end of the previous round and the subsequent division (i.e. in the D period of the division cycle). The cells that initiated were in the D period at the time of addition of the drugs. Rapidly growing cells which normally initiated before the D period and slowly growing cells which normally initiated after the D period did not initiate in the presence of the drugs. The contrasting effects of the drugs in cells possessing different chromosome replication patterns, and the coupling between septum-crosswall formation (the D period) and initiation suggest that the timing of initiation of chromosome replication in E. coli is controlled by the cell envelope.     

Derepression of anthranilate synthase in purified minicells of Escherichia coli containing the Col-trp plasmid

Purified minicells of Escherichia coli K-12 containing the plasmid Col-trp(+) or Col-trpA2 could be derepressed for the synthesis of anthranilate synthase, the first enzyme encoded in the trp operon. Non-plasmid-containing, deoxyribonucleic acid-deficient minicells could not be derepressed. Derepressed enzyme synthesis was initiated by l-tryptophan starvation. The kinetics of derepression were studied with minicells containing the Col-trpA2 plasmid. The derepression curves were biphasic with a rapid initial rate of enzyme synthesis followed by a slower rate of synthesis. The presence of l-tryptophan (20 to 50 mug/ml) or chloramphenicol (200 mug/ml) abolished enzyme synthesis. The presence of rifamycin SV (280 mug/ml) partially inhibited enzyme synthesis after at least 3.5 min of exposure. The ratio of minicell-to-cell synthetic capacity was 1:2.4 when compared on the basis of derepressed enzyme activity per unit cell volume. This work demonstrates that plasmid-containing minicells are capable of considerable functional protein and messenger ribonucleic acid synthesis and that the regulation of at least the trp operon is similar in minicells to that observed in cells.     

Histone-induced changes of protein synthesis inEscherichia coli

The addition of histone to the medium in the logarithmic phase of growth ofEscherichia coli influences alkaline phosphatase synthesis in two ways: it delays initiation of derepression of synthesis of the enzyme by about 60–80 min and it inhibits its synthesis. The inhibitory effect persists even after removing histone from the medium. In stationary-phase of growth the inhibitory effect of histone is obliterated. From an analysis of the initial kinetics of derepressed alkaline phosphatase synthesis and from previous results (?trbáňová-Ne?inováet al., 1972) it is concluded that histone added toEscherichia coli cells interferes with the synthesis of mRNA for alkaline phosphatase.     

Repression and derepression of the enzymes of the pyrimidine biosynthetic pathway in Salmonella typhimurium

Activities of five enzymes of the pyrimidine biosynthetic pathway and one enzyme involved in arginine synthesis were measured during batch culture of Salmonella typhimurium. Aspartate carbamoyltransferase, dihydroorotase, and the arginine pathway enzyme, ornithine carbamoyltransferase, remained constant during the growth cycle but showed a sharp decrease in activity after entering the stationary phase. Dihydroorotate dehydrogenase, orotate phosphoribosyltransferase and orotidine-5'-monophosphate (OMP) decarboxylase showed peaks of activity corresponding to the mid-point of the exponential phase of growth while remaining comparatively stable in the stationary phase. Derepression studies carried out by starving individual pyrimidine (Pyr-) deletion mutants for uracil showed that the extent of derepression obtained for aspartate carbamoyltransferase, dihydroorotase and dihydroorotate dehydrogenase depended on the location of the pyr gene mutation. Orotate phosphoribosyltransferase and OMP decarboxylase derepression levels were independent of the location of the pyr mutation. Aspartate carbamoyltransferase showed the greatest degree of derepression of the six enzymes studied, with pyrA strains (blocked in the first step of the pathway) showing about twice as much derepression as pyrF strains (blocked in the sixth step of the pathway). A study of the kinetics of repression on derepressed levels of the pyrimidine enzymes produced data that were compatible with dilution of specific activity by cell division when repressive amounts of uracil were added to the derepression medium.     

The enzymes of the ammonia assimilation in Pseudomonas aeruginosa

Glutamine synthetase from Pseudomonas aeruginosa is regulated by repression/derepression of enzyme synthesis and by adenylylation/deadenylylation control. High levels of deadenylylated biosynthetically active glutamine synthetase were observed in cultures growing with limiting amounts of nitrogen while synthesis of the enzyme was repressed and that present was adenylylated in cultures with excess nitrogen.NADP-and NAD-dependent glutamate dehydrogenase could be separated by column chromatography and showed molecular weights of 110,000 and 220,000, respectively. Synthesis of the NADP-dependent glutamate dehydrogenase is repressed under nitrogen limitation and by growth on glutamate. In contrast, NAD-dependent glutamate dehydrogenase is derepressed by glutamate. Glutamate synthase is repressed by glutamate but not by excess nitrogen.     

Inactivation of Aspartic Transcarbamylase in Sporulating Bacillus subtilis: Demonstration of a Requirement for Metabolic Energy

The aspartic transcarbamylase (ATCase) activity of Bacillus subtilis cells disappears rapidly from stationary-phase cells prior to sporulation. ATCase activity does not appear in the culture fluid during the stationary phase; hence the enzyme appears to be inactivated in the cells. The enzyme is inactivated normally in two different mutants lacking proteases; the activity is very stable in crude extracts of cells or in the culture fluid. These results suggest that ATCase is not inactivated by the general proteolysis that occurs in sporulating bacteria. The inactivation of ATCase can be completely inhibited after it has begun by oxygen starvation or addition of fluoroacetate. Inhibitors of oxidative phosphorylation and electron transport also interrupt the inactivation of ATCase. The inactivation of ATCase is very slow in two mutant strains that are deficient in enzymes of tricarboxylic acid cycle. Addition of gluconate to stationary cultures of the mutant strains, which is known to restore depleted adenosine 5'-triphosphate pools in these bacteria, also restores inactivation of ATCase. These experiments support the conclusion that the generation of metabolic energy is necessary for the inactivation of ATCase in stationary cells. ATCase activity is stable in growing cells in which ATCase synthesis is repressed by addition of uracil; the enzyme is inactivated normally, however, when such cells cease growing.     

Cytological Studies of Deoxyribonucleic Acid Replication in Escherichia coli 15T−: Replication at Slow Growth Rates and After a Shift-Up into Rich Medium

We examined the gross nuclear morphology of Escherichia coli 15T⁻ grown in different media with doubling times ranging from 22 to 270 min. In slowly growing cells, deoxyribonucleic acid synthesis was measured by autoradiography and shown to occur with greatest probability during the first two-thirds of the division cycle. In such cells, segregation occurred later, at the end of the division cycle rather than at the end of deoxyribonucleic acid replication. Nuclear regions in L-broth cells (22-min doubling time) cannot correspond to separate chromosomes but probably represent regions of replication activity. Segregation of template nucleotide strands was measured after a shift-up from proline M9 or glucose M9 media into L broth. A model is presented to account for the pattern of segregation observed.     

Multiple forms of alkaline phosphatase from Escherichia coli cells with repressed and derepressed biosynthesis of the enzyme.

Isolation of multiple forms of alkaline phosphatase from Escherichia coli cells with repressed and derepressed biosynthesis of the enzyme is reported. Three enzyme forms were isolated from cells with derepressed synthesis, and one form was isolated from cells with repressed enzyme synthesis. The multiple enzyme forms did not differ in pH optimum, thermostability, or the degree of inhibition with orthophosphate; however, they did differ in the relative rate of hydrolysis of different substrates. The addition of substrates to the cells during enzyme derepression resulted in changes of the ratio of the multiple forms.     

X-Ray and Ultraviolet Sensitivity of Synchronously Dividing Escherichia coli

A paper pile filtration technique was used to obtain synchronously dividing populations of E. coli strains B and B/r from cultures in the exponential growth phase. Three generations of highly phased cell division were obtained by rapid pressure filtration which selected approximately 1 per cent of the exponentially growing culture. The sensitivity of E. coli strain B to x-ray and UV inactivation as a function of the cell division cycle was determined on synchronous populations. E. coli strain B showed a sharp decrease in sensitivity to inactivation by both radiations in the middle of the division cycle, and a further decrease near the end of the cycle. The sensitivity of E. coli strain B/r to x-irradiation was also investigated. Only the mid-cycle decrease in sensitivity was found during the division cycle of this strain. It was concluded that the repetition of the observed sensitivity patterns in both strains through the first three cycles after synchronization indicates that the same basic sensitivity patterns are probably also present in the individual cells of an exponential phase culture.     

Crystal structure of Sulfolobus acidocaldarius aspartate carbamoyltransferase in complex with its allosteric activator CTP

Aspartate carbamoyltransferase (ATCase) is a paradigm for allosteric regulation of enzyme activity. B-class ATCases display very similar homotropic allosteric behaviour, but differ extensively in their heterotropic patterns. The ATCase from the thermoacidophilic archaeon Sulfolobus acidocaldarius, for example, is strongly activated by its metabolic pathway′s end product CTP, in contrast with Escherichia coli ATCase which is inhibited by CTP. To investigate the structural basis of this property, we have solved the crystal structure of the S. acidocaldarius enzyme in complex with CTP. Structure comparison reveals that effector binding does not induce similar large-scale conformational changes as observed for the E. coli ATCase. However, shifts in sedimentation coefficients upon binding of the bi-substrate analogue PALA show the existence of structurally distinct allosteric states. This suggests that the so-called “Nucleotide-Perturbation model” for explaining heterotropic allosteric behaviour, which is based on global conformational strain, is not a general mechanism of B-class ATCases.     

Regulation of Cell Division in Escherichia coli: Characterization of Temperature-Sensitive Division Mutants

A temperature-sensitive division mutant of Escherichia coli was isolated by using differential filtration to select for filaments at 42 C and normal cells at 30 C. Cells shifted from 30 to 42 C stop dividing almost immediately, suggesting the temperature-sensitive element is required for cell division late in the cell cycle. Cells returned to 30 from 42 C divide abruptly, suggesting accumulation of division potential at 42 C. Inhibitors of protein, deoxyribonucleic acid, and ribonucleic acid synthesis do not block division during the recovery period at 30 C. Cycloserine does not stop cell division, vancomycin shows some effect on cell division, whereas penicillin completely stops cell division during this period. The addition of high concentrations of NaCl to filaments at 42 C results in a burst of cell division. The final cell number is equivalent to the control which is grown at 30 C if sufficient salt is added (11 g/liter, final concentration). After the original burst, cell division ceases at the nonpermissive temperature even at increased osmolality. Chloramphenicol, puromycin, vancomycin, and penicillin prevent division during the recovery in the presence of NaCl. Kinetic data indicate division potential decays to a reversible inactive intermediate which rapidly decays to an irreversible inactive form. Conversion of division potential to the inactive form is correlated with a 100- to 1,000-fold derepression of the synthesis of division potential. The mutation appears to involve a stage in cross-wall synthesis which is required during the terminal stages of division.     

Comparison of Patterns of Accumulation of Ribulose Bisphosphate Carboxylase Antigen and Catalytic Activity and Measurement of Antigen Half-Life during the Cell Cycle of Chlorella sorokiniana

By use of specific immunochemical procedures, ribulose-1,5-bisphosphate carboxylase (RuBPCase), antigen and catalytic activity were shown to have coincident step-patterns of accumulation during the cell cycle of Chlorella sorokiniana. Pulse-chase studies, employing radioactive sulfate, were performed during the period of rapid accumulation of enzyme activity and during the period of constant enzyme activity in the cell cycle. No degradation of RuBPCase antigen could be detected during either of these cell cycle periods. Thus, the step-pattern of accumulation of RuBPCase activity resulted from periodic synthesis of an enzyme that was stable under steady-state cell cycle conditions. Although inhibition of protein synthesis by cycloheximide, at different times in the cell cycle in the light, resulted in rapid decay of RuBPCase activity, this loss in activity occurred without detectable loss in enzyme antigen. When synchronous cells were placed into the dark, to slow the rate of protein synthesis in the absence of cycloheximide, the levels of enzyme antigen and activity decreased by 30 and 50%, respectively, during the 10-hour dark period. Thus, in C. sorokiniana changes in RuBPCase activity do not necessarily reflect parallel changes in enzyme antigen, particularly when cell growth is perturbed by changes from steady-state cultural conditions.     

Phenylalanine Biosynthesis in Escherichia coli K-12: Mutants Derepressed for Chorismate Mutase P-Prephenate Dehydratase

Mutants were isolated which are derepressed for the synthesis of chorismate mutase P-prephenate dehydratase. No other enzymes involved in the synthesis of phenylalanine are derepressed in these strains. These mutants are able to grow in concentrations of o- and p-fluorophenylalanine that inhibit the growth of AB3259, the strain from which they were derived. They also excrete phenylalanine. Genetic analysis shows that the mutations causing this derepression are closely linked to the structural gene for this enzyme (cotransduction frequency of 95% or more with pheA). The gene in which they occur has been designated pheO since this gene has all of the properties predicted for an operator gene controlling the pheA structural gene. Finally, the pheO mutant alleles have been shown to be dominant in diploids.     

A positive regulatory gene is required for accumulation of the functional messenger RNA for the glucose-repressible alcohol dehydrogenase from Saccharomyces cerevisiae

The amount of glucose-repressible alcohol dehydrogenase is regulated by the amount of its functional messenger RNA. ADHII² protein was detected by a radioimmune assay and differentiated from ADHI, the classical ADH isozyme, by limited proteolysis with Staphylococcus aureus protease. When yeast containing the wild-type alleles for ADR2 (the ADH II structural locus) and for ADR1 (its positive regulatory gene) were pulse-labeled with [³⁵S]methionine during derepression, radioactive label accumulated in the antibody-precipitated ADHII coterminously with the appearance of ADHII activity. The kinetics of functional ADHII mRNA appearance during derepression in this strain were shown to be the same as those for ADHII protein synthesis in vivo when RNA, extracted from derepressed cells, was translated in a wheat germ cell-free translation system.The role of the positive regulatory gene, ADR1, in ADHII expression was analyzed using two strains mutated at that locus. Yeast containing the adr1-1 allele are incapable of derepressing ADHII activity. When this strain was pulselabeled with [³⁵S]methionine during derepression, approximately one-tenth to one-twentieth the level of ADHII protein synthesis was detected as in the wild-type strain. When RNA was extracted during derepression from cells containing the udr1-1 allele and translated in a wheat germ cell-free system, little functional ADHII mRNA was found to be present.The role of the ADR1 gene was further analyzed using a strain containing the ADR1-5^c allele, which allows constitutive synthesis of ADHII activity. In this strain during glucose repression. ADHII protein synthesis and amount of functional mRNA were at levels comparable to those found for the wild-type strain after complete derepression. Similar kinetics of ADHII protein synthesis and of mRNA accumulation during derepression were observed in the strain carrying the ADR1-5^c allele when compared to that carrying the ADR1 allele, but the absolute amounts were greater by three- to fourfold in cells containing the ADR1-5^c allele. These results indicate that the ADR1 gene acts to increase the level of functional ADHII mRNA during derepression.