Regulation of ribonucleic acid synthesis in growing bacterial cells: I. Control over the total rate of RNA synthesis

Abstract

It is well known that bacterial cells regulate their rate of RNA accumulation (net RNA synthesis) in strict accord with the potential of a particular medium to support growth at a given rate, and that in shifts from one medium to another there are rapid and seemingly preferential changes in the net rate, while the other parameters of cell growth change more slowly. In this study, in addition to making measurements of net rates of RNA synthesis in steady states and shifts from one medium to another, measurements of the total rate, that is the sum of the rates of synthesis of stable and unstable RNA species, are made. This is done by measuring the early slope of the incorporation of a radioactive precursor ([ 3H]guanine) into RNA, and correcting for the specific activity of the intracellular precursor ([ 3H]GTP) at those times. It is found that, in differing steady states of growth, cells vary, not only their total rate of RNA synthesis, but also the fraction of the total given to the formation of unstable species. Expressed as a ratio of stable to unstable RNA's, this latter value is about one to one in minimal-glucose and two to one in medium enriched with amino acids. Moreover, transients between steady states give a stronger indication that the synthesis of stable and unstable RNA species can vary independently. In shift-up for example, while the net rate of accumulation, presumably largely the synthesis of the stable ribosomal and transfer RNA's, increases immediately, giving rise to the striking increase of isotope uptake known to take place, the rate of total synthesis increases only in the course of 5 to 15 minutes, such that at early times the ratio of stable to unstable RNA's made reaches about three to one. These experiments suggest that the mechanism for the control of RNA synthesis involves both a means whereby the total capacity of the cell to make RNA is limited, as well as a mechanism by which the distribution of that capacity between template sites leading to the synthesis of stable and unstable RNA species is regulated.