Synthesis of messenger RNA coding for individual ribosomal proteins during nutritional shift-up in Escherichia coli K-12

Abstract

The rates of increase in mRNA content coding for the individual ribosomal proteins were measured in Escherichia coli K-12 following a nutritional shift-up. Messenger RNA synthesis was arrested by the inhibitor thiolutin and the amount of protein synthesized from the pre-existing mRNA was used as a measure of mRNA content. The data obtained show, with the exception of protein S2, a rapid increase in the mRNA content during the first 7 min after shift-up followed by a slower rate of increase during the period 7–30 min. The amount of protein S2-specific mRNA increased at a rate that remained constant over the entire 0–30 min period. Among the remaining ribosomal protein cistrons a variety of rates of transcription was obtained during both the early and later periods; these rates were not related to the amount of mRNA present immediately prior to shift-up. The significance of the anomalous behaviour of protein S2 is discussed as well as the change in rate of mRNA synthesis observed for the remainder of the ribosomal proteins at about 7 min following shift-up. The results are discussed in relation to other data on the regulation of ribosomal protein synthesis and to the grouping of cistrons into transcriptional units.