Regulation of ribonucleic acid synthesis in growing bacterial cells. II. Control over the composition of the newly made RNA

Studies have been made by base-ratio analysis and DNA-RNA hybridization of the pulse-labeled, nascent RNA in cells of Escherichia coli growing exponentially in minimal-glucose and Casamino acids-supplemented media, as well as during shift-ups or shift-downs between them. It is found that the cell varies the fraction of the newly made RNA given over to the synthesis of ribosomal and (presumably) transfer RNA under these different conditions. Furthermore, for cells in exponential growth or during shift-up, these values are in good agreement with the amount of “stable” RNA made as defined in the kinetic experiments in the accompanying paper. Thus under these conditions, there is no need to postulate the existence of a mechanism involving the rapid destruction of otherwise stable RNA's, a situation which may occur in shift-down or other growth conditions.