The Rates of Synthesis and Chain Elongation of Ribonucleic Acid in Escherichia coli

Abstract

Abstract The synthesis of RNA in two strains of Escherichia coli 15 TAU and CP 78, has been studied. With 3H-uracil-labeling data and the measured specific activity of cellular UTP pools over very short labeling periods at 27°, several observations have been made. 1. The initial observed rate of RNA synthesis is approximately 2.7 times faster than the rate of accumulation of stable RNA. Thus, about 60% of the cellular capacity for RNA synthesis is devoted to production of mRNA. 2. The number of nascent RNA chains in 15 TAU and CP 78 is 5100 chains per cell and 2500 chains per cell, respectively. 3. The two strains of E. coli had different growth rates and different observed rates of RNA synthesis, but the rates of chain elongation were 20 nucleotides per sec per chain for 15 TAU and 23 nucleotides per sec per chain for CP 78. This observation suggests that cellular control of the rate of RNA synthesis operates via regulation of the number of nascent chains, not their rate of elongation. 4. It is estimated that RNA polymerase molecules involved in the synthesis of ribosomal RNA are spaced at approximate intervals of 80 DNA base pairs and that these cistrons must be transcribed tandemly by multiple molecules simultaneously.