Turnover of ribosomal RNA during the stringent response in Escherichia coli

Abstract

In order to establish whether turnover of ribosomal RNA occurs during aminoacid starvation, the following parameters were measured in growing Escherichia coli cells and in cells starved of amino acids: (1) the net rate of synthesis of ribosomal and transfer RNA, (2) the rate of synthesis of nascent RNA, and (3) the fraction of nascent RNA which is ribosomal and transfer RNA. Amino-acid starvation was elicited by effecting the deacylation of a species of transfer RNA in a bacterial strain harboring a heat-sensitive aminoacyl-transfer RNA synthetase. The net rate of synthesis of ribosomal and transfer RNA in the cells starved of amino acids was found to be 1.8% of that in growing cells. The rate of synthesis of nascent RNA in the starved cells is either 64% or 165% of the rate in growing cells, depending on the method used for measurement. Two RNA-DNA hybridization techniques gave values of 45% or 46% for the percentage of nascent RNA which is ribosomal or transfer RNA in growing cells, and 34% or 25% for the percentage of nascent RNA which is ribosomal or transfer RNA in the starved cells. It is concluded from these data that between 35% and 100% of the inhibition of net RNA synthesis observed in cells starved of amino acids is attributable to turnover of ribosomal RNA and, perhaps, transfer RNA.