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

R M Winslow,R A Lazzarini

doi:10.1016/s0021-9258(18)91817-x

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.

Highlights

The synthesis of RNA in two strains of Escherichia coli 15 TAU and CP 78, has been studied
About 60% of the cellular capacity for RNA synthesis is devoted to production of mRNA
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 set per chain for 15 TAU and 23 nucleotides per set 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

Summary

Methods

GeneralOutline of Method-The method used depends on the facts that nascent (still growing) RNA chains are elongated by the addition of nucleotide monophosphate residues to the 3’ The rate of RNA synthesis in the bacterial cell is the product ends (7, 8) and that after alkaline hydrolysis the 3’-hydroxyl of two general factors: the number of RNA chains under con- termini of these nascent chains can be recovered as nucleosides, struction and the average rate at which nucleotide residues whereas internal residues appear as nucleotides. The latter has been most frequently idealized model illustrating this method. The rate of chain elongation at 37” for ribosomal after addition of labeled precursor, only points of chain growth RNA has been estimated at 80 nucleotides per see in Bacillus are labeled. The size of this (3) and tryptophanase (4) are assembled at a rate of 25 nucleo- nucleoside fraction increases only as a result of chain completion tides per see at 25”. The line obtained by plotting and Yuan (5, 6) indicate that mRNA of T4-infected E. cola’ nucleosides against time should have an ordinate intercept

Results

Discussion

Conclusion