Kinetic studies on the relationship of ribonucleotide precursor pools and ribonucleic acid synthesis

Abstract

A study has been made of the kinetics of flow of [ 14C]uracil through the intracellular pools of pyrimidine ribonucleotides of Bacillus subtilis. The rate at which these pools fill is slow as compared to that predicted from the measured sizes of these pools and the rate of nucleic acid synthesis. These results may be a consequence of the continued entry of uracil derivatives into the pools from messenger RNA turnover, or alternatively due to an internal compartmentalization of the pool components. The uracil derivatives (UMP, UDP, UTP, UDPG), which make up about 75% of the total pool size, are rapidly equilibrated with one another; this is seen in the fact that one can only trace a sequential flow of radioactive uracil through them in experiments at lowered temperatures. On the other hand, the kinetics of uracil flow through the soluble pools is the same as that through messenger, which is consistent with the equilibration of the two through messenger turnover and recycling of isotope from the pools into the messenger. By measuring the rate of [ 14C]uracil entry into the pools, and the size of the pools, an estimate of the size of that fraction of the RNA of the cells that is turning over is obtained (7%), which is in agreement with the value obtained with the aid of actinomycin D.