. Cell heredity. Cytogenetics. 322 CELL HEREDITY 280. 480 FIGURE Induction of galactoz/mase in /east cells in the presence and absence of a nitrogen source. Yeast cells grown on glucose have no galoctozymase activity, but following the addition of galactose, enzyme formation begins. Within 4 hours, con- siderable enzyme is formed both in the presence and absence of a nitrogen source. These results indicate that a new enzymatic activity can appear in nondividing or scarcely dividing cells (after Spiegelman, 1946, C. S. H. Symp. Quanf. Biol., 11:256). gene action, and regulatory mechanisms
. Cell heredity. Cytogenetics. 322 CELL HEREDITY 280. 480 FIGURE Induction of galactoz/mase in /east cells in the presence and absence of a nitrogen source. Yeast cells grown on glucose have no galoctozymase activity, but following the addition of galactose, enzyme formation begins. Within 4 hours, con- siderable enzyme is formed both in the presence and absence of a nitrogen source. These results indicate that a new enzymatic activity can appear in nondividing or scarcely dividing cells (after Spiegelman, 1946, C. S. H. Symp. Quanf. Biol., 11:256). gene action, and regulatory mechanisms of metabolic control at the cellular level. In what follows, we shall attempt neither a chrono- logical development of the subject nor a comprehensive summary of the field, but rather a sketch of those findings and related concepts which appear to be central to the analysis of mechanisms of genetic control. The most extensive, systematic, and diversified analysis of enzyme formation has been performed by Monod and collaborators over a period of many years at the Pasteur Institute, focusing primarily upon the |3-galactosidase enzyme of E. coli. Other contributions of central im- portance have come from Spiegelman's studies with yeast, and Pollock's investigations of penicillinase formation in the bacterium Bacillus cereus. Consider a population of yeast cells growing in liquid culture with glucose as their carbon source. They are washed, and half of them are resuspended in a growth medium containing galactose as sole carbon source, the other half in a medium with galactose but no nitrogen source to prevent growth. The resulting increase in activity of the galactose- fermenting enzyme, galactozymase, is shown in Figure Almost as. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sager, Ruth; Ryan, Francis
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