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SUMMARY : No P-galactosidase was formed when nitrogen-depleted cells of Escherichia coli 1433 were treated with lactose unless a source of nitrogen was added to the cells. In the presence of an exogenous nitrogen source there was an appreciable delay between the addition of lactose and the appearance of induced P-galactosidase activity. In contrast, induced increases of nitrate- and tetrathionate-reductase activities were developed without appreciable delay when depleted cells were treated with nitrate and tetrathionate, respectively, in the absence of additional nitrogen sources. The total amounts of the reductase activities developed in depleted cells were Iess than those obtained with non-depleted cells. The total amount of nitrate reductase activity formed was only slightly increased in the presence of ammonium sulphate, whereas normal degrees of activity were attained in the presence of casein hydrolysate. Ammonium sulphate markedly stimulated the formation of tetrathionate reductase activity. Conclusive evidence has been presented (Monod & Cohn, 1953 ; Hogness, Cohn & Monod, 1955; Rotman & Spiegelman, 1954) that under certain conditions cells of Escherichia coli do not contain appreciable amounts of complex precursors of the inducible (adaptive) ,8-galactosidase. Similarly, for the inducible maltozymase system of Saccharomyces cerevisiae, Halvorson & Spiegelman (l952,1953a, b; Spiegelman & Halvorson, 1953) concluded that induced enzyme is probably not formed via complex precursors that are normally present in non-induced cells. It has, therefore, been suggested (Monod & Cohn, 1953; Rotman & Spiegelman, 1954) that the process of induced enzyme formation is essentially one of de novo synthesis entirely from free amino acids. However, the maltozymase system of Saccharornyces cerevisiae is unstable and can be degraded even by cells which are not depleted of nitrogen reserves (Spiegelman & Dunn, 1947). Hence, as noted by Spiegel- man & Halvorson (1953), the information obtained to date for this system cannot be considered as critical evidence of the absence of complex enzyme precursors from the cells. The processes of induced P-galactosidase synthesis in Escherichia coli differ in a number of respects from those of induced formation of other systems. For example, little P-galactosidase synthesis can occur in suspensions of well- washed cells of E. coli (Cohn & Torriani, 1953), whereas considerable forma- tion of the nitrate and tetrathionate reductase (nitratase and tetrathionase)

The Influence of Depletion of Nitrogenous Reserves upon the Phenomenon of Induced Enzyme Biosynthesis in Cells of Escherichia coli