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L B Rothman-Denes

Publications and source records attributed to L B Rothman-Denes.

50 records · Page 3Linked to original sources
PubMed1978

Novel template requirements of N4 virion RNA polymerase.

A DNA-dependent RNA polymerase has been purified from disrupted virions of the Escherichia coli bacteriophage N4. The RNA polymerase is phage-coded and is required for class I N4 RNA synthesis, which is defined as RNA synthesized in vivo in the absence of post-infection protein synthesis. A polypeptide of molecular weight 350,000 is detected when the purified enzyme is analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. N4 RNA polymerase requires denatured DNA as a template in vitro and shows a strong preference for denatured N4 DNA. With this template, transcription is asymmetric. The RNA product is complementary to only the H strand of N4 DNA. Furthermore, only class I N4 RNA is synthesized. In vivo transcription by the N4 virion RNA polymerase is inhibited by coumermycin. This result suggests that the activity of E. coli DNA gyrase, an enzyme that introduces negative supertwists into DNA, is required for N4 transcription.

Coliphages↗
PubMed1977

Virion-associated RNA polymerase required for bacteriophage N4 development.

Escherichia coli phage N4 transcription is resistant to rifampicin, an inhibitor of the host RNA polymerase, even when the drug is added prior to infection. A rifampicin-resistant RNA polymerase has been detected in disrupted N4 virions. This enzyme shows a requirement for the four ribonucleoside 5'-triphosphates and exogenous denatured DNA. With denatured N4 DNA, the preferred template, transcription is asymmetric. The virion RNA polymerase apparently is necessary for phage development because a conditional lethal N4 mutant shows temperature-sensitive RNA synthesis in vivo as well as a temperature-sensitive RNA polymerase in disrupted virions.

Binding, Competitive↗
PubMed1975

Adenosine 3':5'-cyclic monophosphate as mediator of catabolite repression in Escherichia coli.

Measurements of intracellular adenosine 3':5'-cyclic monophosphate (cAMP) concentrations in E. coli under a variety of conditions show that levels of this nucleotide are well correlated with the rate of synthesis of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) in both catabolite repression and transient repression. These results, combined with extensive genetic and in vitro studies from a number of laboratories on the role of cAMP in E. coli, provide strong support for the concept that intracellular cAMP levels mediate the effects of catabolite and transient repression on rates on enzyme synthesis. Under all conditions studied, excretion can be described by a single rate constant, 2.1 min-1 at 37 degrees, indicating that intracellular levels cannot be regulated by alterations in the rate of cAMP excretion. Our data are fully consistent with the idea that carbon sources control intracellular cAMP levels by effects on its synthesis.

Cyclic AMP↗
PubMed1973

Role of cyclic adenosine 3',5'-monophosphate in the in vivo expression of the galactose operon of Escherichia coli.

Studies of levels of galactokinase in Escherichia coli with mutations affecting synthesis of, or response to, cyclic adenosine 3',5'-monophosphate show that this nucleotide does not play a major role in expression of the galactose operon, causing at most a twofold stimulation. The discrepancy between our in vivo results and the marked stimulation by cyclic adenosine 3',5'-monophosphate in in vitro systems indicates that current cell-free systems lack a factor which allows efficient expression of the galactose operon even in the absence of cyclic adenosine 3',5'-monophosphate or of the binding protein for this nucleotide.

Carbon Isotopes↗
PubMed1973

Protein synthesis.

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Peptide Biosynthesis↗
PubMed1970

Two forms of yeast glycogen synthetase and their role in glycogen accumulation.

The glycogen content of yeast rises dramatically just before the onset of the stationary phase of growth. Concomitantly, a rapid increase was found in the glucose 6-phosphate-independent (I) activity of glycogen synthetase, as well as in the total amount of enzyme. A mutant (GS 1-36) was obtained, which did not accumulate glycogen during growth. The synthetase from this strain was in the glucose 6-phosphate-dependent (D) form at all times. The total enzymatic activity of the mutant also increased sharply at the end of the logarithmic phase, although its maximal value was only one third that of the parent strain. Incubation with glucose of wild type resting cells from the logarithmic phase resulted in a slow accumulation of glycogen, which was accelerated after 20 min. At the same time a transformation from the D to I form of the enzyme was detected. The same slow initial rate of glycogen deposition was found with stationary cells of mutant GS 1-36, but the rate gradually declined to zero, rather than accelerating. The interconversion of the I and D forms was obtained with extracts from cells harvested during different phases of growth. Examination of the properties of the I and D forms showed that the latter was much more strongly inhibited by ATP at low glucose 6-phosphate concentration. These findings clearly establish the fundamental role of the I form in glycogen accumulation. When taken together with previous results, they also show that the physiological significance of the I-D interconversion depends on the concentration of glucose 6-phosphate. Under certain conditions glucsoe 6-phosphate appears to regulate directly the activity of the predominant form of the enzyme.

Adenosine Triphosphate↗