Kinetic Evidence for a Nucleic Acid which regulates RNA Biosynthesis

Abstract

THE rate of synthesis of nucleic acids in Escherichia coli strain B_u⁻ has been examined in a variety of situations by measuring the incorporation into TCA insoluble material of 20-sec pulses of ¹⁴C-8-guanine. In most cases the 20-sec pulses are long enough to give useful amounts of incorporations. However, extensive washing of the ‘Millipore’ filters must be carried out and frequently long counting times must be used. There is a short lag in the utilization of ¹⁴C-8-guanine, but under most conditions 20 sec gives about half the radioactivity which would have been estimated from the rate of incorporation at later times, that is, there is about 10–13 sec worth of materials in pools already present in the cell, or made before feed-back inhibition becomes effective. Incorporation of radioactivity is the same at 0.1 the external concentration of ¹⁴C-8-guanine as that standardly employed (5 µM), implying that feed-back inhibition is under both conditions maximal and rapid.