Signaling Recognition Events with Fluorescent Sensors and Switches.

https://www.mun.ca/biology/scarr/Jacob_&_Monod_(1961)_presentation.pdf

Genetic regulatory mechanisms in the synthesis of proteins.

Clonal populations of cells exhibit substantial phenotypic variation. Such heterogeneity can be essential for many biological processes and is conjectured to arise from stochasticity, or noise, in gene expression. We constructed strains of Escherichia coli that enable detection of noise and discrimination between the two mechanisms by which it is generated. Both stochasticity inherent in the biochemical process of gene expression (intrinsic noise) and fluctuations in other cellular components (extrinsic noise) contribute substantially to overall variation. Transcription rate, regulatory dynamics, and genetic factors control the amplitude of noise. These results establish a quantitative foundation for modeling noise in genetic networks and reveal how low intracellular copy numbers of molecules can fundamentally limit the precision of gene regulation.

https://science.sciencemag.org/content/sci/297/5584/1183.full.pdf

Stochastic Gene Expression in a Single Cell

Genetically identical cells exposed to the same environmental conditions can show significant variation in molecular content and marked differences in phenotypic characteristics. This variability is linked to stochasticity in gene expression, which is generally viewed as having detrimental effects on cellular function with potential implications for disease. However, stochasticity in gene expression can also be advantageous. It can provide the flexibility needed by cells to adapt to fluctuating environments or respond to sudden stresses, and a mechanism by which population heterogeneity can be established during cellular differentiation and development.

/pdf/stochasticity-in-gene-expression-from-theories-to-phenotypes-32urfuz0k3.pdf

Stochasticity in gene expression: from theories to phenotypes

Intracellular pH measurements in Ehrlich ascites tumor cells utilizing spectroscopic probes generated in situ.

https://www.pnas.org/content/pnas/55/1/134.full.pdf

Membrane properties of living mammalian cells as studied by enzymatic hydrolysis of fluorogenic esters.

https://www.pnas.org/content/pnas/47/12/1981.full.pdf

MEASUREMENT OF ACTIVITY OF SINGLE MOLECULES OF β-D-GALACTOSIDASE

Transport systems for galactose and galactosides in Escherichia coli. II. Substrate and inducer specificities.

Recently reported experiments have made it necesary to assume that the induced synthesis of enzymes in microorganisms is coupled mandatorily to the utilization of free amino acids. Investigations (Halvorson and Spiegelman, 1952) with yeast have shown that analogues of amino acids which prevent incorporation from the free amino acid pool into protein also suppress the induced formation of a-glucosidase. Furthermore, a complete parallelism between a-glucosidase synthesizing capacity and the available internal supply of free amino acids was demonstrated by means of depletion and replenishment cycles (Halvorson and Spiegelman, 1953a). Finally, employing the same sstem, it was posible to exhibit (Halvorson and Spiegelman, 1953a) a net increased utilization of the intemal free amino acids as a consequence of the induction of enzyme synthesis in cells suspended in a nitrogen-free medium. The generality of the findings with amino acid analogues was extended by the independently performed experiments of Lee and Williams (1952). These authors demonstrated that the administration of ethionine to the intact rat prevented the induced formation of tryptophan peroxidase. Monod et al. (1952) studied the formation of ft-galactosidase in a series of amino acid auxotrophic mutants of Eecherichia coli. In no case was enzyme synthesis observed in the absence of the particular amino acid required. Rickenberg et al. (1953) report experiments along similar lines in which f3-galactosidase formation was 1 This research was aided by a grant from the National Cancer Institute of the National Institutes of Health and by a contract between the Office of Naval Research, Department of the Navy, and the University of Illinois, NR 135-136. 2 A summary of the present results was presented at the 1953 meeting of the Society of American Bacteriologists (Bacteriol. Proc., 1953, p. 92). ' Present address: Enzyme Institute, Madison, Wisconsin. followed in mutant strains of B. coli, strain K-12. Analogous reults also were obtained in the induction of a myoinositol degradation system in Aerobacter aerogenae (Ushiba and Mag ik, 1952). The data cited would appear to eliminate any mechaism of enzyme synthesis which involves an amino acid independent transformation of a preexistent complex precursor into active enzyme. They do not, however, make untenable, or distinguish between, the following two possibilities for enzyme synthesis: (a) Precursor and free amino acids --+ Active enzymes. (b) Free amino acids -* Active enzyme. It is the purpose of the present paper to offer data relevant to this issue. The most obvious experimental approach aimed at a decision between the above two alternatives would appear to be the use of isotopic labels. Thus, the induction of enzyme synthesis in uniformly labeled cells suspended in unlabeled medium should provide the necesary data. It is evident from the type of experiment contemplated that the presence of a large internal free amino acid pool, such as exists in the yeasts and many gram positive bacteria, would introduce a complication which could well make the data uninterpretable. To avoid this complication, attention was turned to enzyme formation in gram negative microorganisms which have been shown (Taylor, 1947) to lack detectable free amino pools. The system selected for study was the,-galactosidase of E. coli. The choice of this particular enzyme was dictated by a variety of reasons. Lederberg (1950) devised a convenient and accurate assay of its activity by employing the synthetic chromogenic substrate o-nitrophenyl-,B-D-galactoside. In addition, the intensive investigations to which this system in E. coli has been subjected in recent years have elucidated not only purely enzymatic properties (Cohn and Monod, 1951; Kuby and Lardy, 1953; Lester and

ON THE ORIGIN OF THE CARBON IN THE INDUCED SYNTHESIS β-GALACTOSIDASE IN ESCHERICHIA COLI

https://www.pnas.org/content/pnas/50/1/1.1.full.pdf

Boris Rotman

Papers

Membrane properties of living mammalian cells as studied by enzymatic hydrolysis of fluorogenic esters.

MEASUREMENT OF ACTIVITY OF SINGLE MOLECULES OF β-D-GALACTOSIDASE

Transport systems for galactose and galactosides in Escherichia coli. II. Substrate and inducer specificities.

ON THE ORIGIN OF THE CARBON IN THE INDUCED SYNTHESIS β-GALACTOSIDASE IN ESCHERICHIA COLI

FLUOROGENIC SUBSTRATES FOR β-D-GALACTOSIDASES AND PHOSPHATASES DERIVED FROM FLUORESCEIN (3, 6-DIHYDROXYFLUORAN) AND ITS MONOMETHYL ETHER