THE CONTROL OF SULPHATE REDUCTION IN BACTERIA

1. An enzyme from Escherichia coli 9723 that reduces adenosine 3'-phosphate 5'-sulphatophosphate to inorganic sulphite is described. Extracts of E. coli K(12) and Bacillus subtilis 1379 contain a similar enzyme. 2. This reductase and sulphite reductase (EC 1.8.1.2) of E. coli 9723, E. coli K(12) and of B. subtilis are repressed by growth in the presence of l-cystine. Cysteine synthase (EC 4.2.1.22) is unaffected. 3. Growth of E. coli 9723 on inorganic sulphite represses the sulphate-activating enzymes (EC 2.7.7.4 and 2.7.1.25) almost completely but has little effect on sulphite reductase. Growth on 0.042-0.056mm-l-cystine gives a similar result. 4. Such differential repression by cyst(e)ine prevents E. coli, when growing on sulphite, from synthesizing unnecessary enzymes.

REGULATORY MECHANISMS IN THE BIOSYNTHESIS OF ISOLEUCINE AND VALINE. II. IDENTIFICATION OF TWO OPERATOR GENES

Ramakrishnan, T. (Yale University, New Haven, Conn.), and Edward A. Adelberg. Regulatory mechanisms in the biosynthesis of isoleucine and valine. II. Identification of two operator genes. J. Bacteriol. 89:654-660. 1965.-A tightly clustered set of five structural genes governs the synthesis of the five enzymes of isoleucine and valine biosynthesis in Escherichia coli. Three of the genes governing transaminase B, dehydrase, and threonine deaminase, are controlled by a single operator locus, designated oprA. The structural gene governing the condensing enzyme is controlled by a second operator locus, designated oprB. Both oprA and oprB have been shown to regulate structural genes which are cis, but not trans, to their own operator. No mutations have yet been found which affect the level of reductoisomerase, but the existence of a third operator controlling the synthesis of this enzyme can be inferred. Enzyme derepression resulting from mutations in oprA confers resistance to high levels of valine. Derepression of the condensing enzyme resulting from mutations in oprB confers resistance to low levels of valine, and to alpha-aminobutyric acid. The significance of these findings with respect to the valine sensitivity of E. coli strain K-12 is discussed.

THE BIOSYNTHESIS OF ALKALINE PHOSPHATASE WITH A PARTICULATE FRACTION OF ESCHERICHIA COLI

1. By digitonin lysis of penicillin spheroplasts of Escherichia coli a particulate fraction P(1) was previously obtained that supported the sustained synthesis of alkaline phosphatase when supplied with amino acids, nucleotide triphosphates and other cofactors. This P(1) fraction, when subjected to mild ultrasonic treatment in the presence of sucrose and Mg(2+), yielded the P(1)(S) fraction, consisting of integrated particulate subcellular particles containing DNA and RNA. 2. The P(1)(S) fraction from E. coli K10 wild type (R(+) (1)R(+) (2)P(+)) grown under repressed conditions supported the immediate synthesis of alkaline phosphatase in vitro. The synthesis occurred in phases. The first was followed by a lag, and then there was a linear rapid phase that continued for at least 3hr. Actinomycin D inhibited the appearance of the second phase. It was concluded that the particles are programmed to synthesize enzyme even when prepared from repressed cells, and therefore that synthesis of the specific messenger RNA for alkaline phosphatase in vivo was not inhibited when the bacteria were grown in an excess of inorganic phosphate. 3. Phosphate inhibited synthesis of enzyme to the same extent with the P(1)(S) fractions of two constitutive strains as with the P(1)(S) fraction of the wild-type strain. 4. Inorganic phosphate inhibited amino acid incorporation with the P(1)(S) fraction and also inhibited enzyme synthesis in vitro. The effect on amino acid incorporation could be partially overcome by adding Mn(2+) to the incubation mixtures. However, Mn(2+) inhibited the synthesis of alkaline phosphatase. Also, inhibition of the incorporation of [(32)P]CTP into RNA was overcome by Mn(2+). The effect of phosphate on amino acid uptake was most probably due to a phosphorolysis of RNA by polynucleotide phosphorylase, also present in the P(1)(S) fraction. This phosphorolysis may be responsible for the instability of messenger RNA in vitro and in vivo. 5. Phosphate also specifically inhibited the formation of alkaline phosphatase, since it did not affect markedly the induced formation of beta-galactosidase by the same P(1)(S) fraction. The specific effect is attributed to the prevention of formation of the enzymically active dimer from precursors, a Zn(2+)-dependent reaction. It is suggested that the repression of the synthesis of alkaline phosphatase in vivo in the wild-type strain was the sum of these two effects.

FURTHER STUDIES ON THE REGULATION OF AMINO SUGAR METABOLISM IN BACILLUS SUBTILIS

1. Glucosamine 6-phosphate deaminase [2-amino-2-deoxy-d-glucose 6-phosphate ketol-isomerase (deaminating), EC 5.3.1.10] of Bacillus subtilis has been partially purified. Its K(m) is 3.0mm. 2. Extracts of B. subtilis contain N-acetylglucosamine 6-phosphate deacetylase (K(m) 1.4mm), glucosamine 1-phosphate acetylase and amino sugar kinases (EC 2.7.1.8 and 2.7.1.9). 3. Glucosamine 6-phosphate synthetase (l-glutamine-d-fructose 6-phosphate aminotransferase, EC 2.6.1.16) is repressed by growth of B. subtilis in the presence of glucosamine, N-acetylglucosamine, N-propionylglucosamine or N-formylglucosamine. Glucosamine 6-phosphate deaminase and N-acetylglucosamine 6-phosphate deacetylase are induced by N-acetylglucosamine. Amino sugar kinases are induced by glucose, glucosamine and N-acetylglucosamine. The synthesis of glucosamine 1-phosphate acetylase is unaffected by amino sugars. 4. Glucose in the growth medium prevents the induction of glucosamine 6-phosphate deaminase and of N-acetylglucosamine 6-phosphate deacetylase caused by N-acetylglucosamine; glucose also alleviates the repression of glucosamine 6-phosphate synthetase caused by amino sugars. 5. Glucosamine 6-phosphate deaminase increases in bacteria incubated beyond the exponential phase of growth. This increase is prevented by glucose.

THE CONTROL OF SULPHATE ACTIVATION IN BACTERIA

1. ATP-sulphate adenylyltransferase (EC 2.7.7.4) and ATP-adenylyl sulphate 3'-phosphotransferase (EC 2.7.1.25) of Escherichia coli 9723, E. coli K(12) and Bacillus subtilis 1379 are each repressed by growth in the presence of cystine. Repression of the two enzymes in E. coli 9723 may be co-ordinate. 2. ATP-sulphate adenylyltransferase of Desulphovibrio desulphuricans, in which sulphate reduction is linked to the energy supply of the organism, is not repressed by growth in the presence of inorganic sulphite or cysteine. 3. Leuconostoc mesenteroides lacks all the enzymes between sulphate and cysteine whether grown on cysteine or glutathione.

INDUCTION AND MULTI-SENSITIVE END-PRODUCT REPRESSION IN THE ENZYMIC PATHWAY DEGRADING MANDELATE IN PSEUDOMONAS FLUORESCENS

1. The first five enzymes involved in the degradation of mandelate in Pseudomonas fluorescens have been examined. 2. Induction is not significantly affected by glucose. 3. The first three enzymes form a group inducible by mandelate and repressible by benzoate, catechol and succinate. 4. The possibility that benzoate and catechol act as repressors only after they have been degraded to succinate is unlikely since mutants blocked at suitable points in the pathway have the same repression pattern as the wild type. 5. It is concluded that synthesis of the enzymes is subject to a multi-sensitive repression mechanism that can be independently activated by benzoate or catechol or succinate. 6. In each case the repression can be largely overcome by increasing the concentration of the inducer. 7. The enzymes of the first group are thus controlled by a dual system in which induction by the first substrate is opposed by repression exerted by the end product of the first group and by the products of succeeding groups.