Biosynthesis of RNA polymerase in Escherichia coli

Abstract

The synthesis rate, content and intracellular distribution of the DNA-dependent RNA polymerase were determined for wild-type cells of Escherichia coli under various phases of growth. The differential rate of synthesis decreases during the transition to the stationary phase first for RNA polymerase α subunit and ribosomal proteins and subsequently for ββ′ subunits, whereas the rate of σ subunit synthesis remains virtually constant throughout the growth. In consequence, the synthesis ratio among RNA polymerase subunits varies depending on the phase of cell growth: In the exponentially growing phase, α and σ subunits are synthesized in excess of of less than ββ′ subunits, respectively, on a molar basis; in contrast, nearly stoichiometric amounts are synthesized for all four subunits (1β′, 1β, 1σ and 1α) in the stationary phase. The decrease in the syntehsis rate of core enzyme subunits as well as the degradation of both newly synthesized and pre-existing ββ′ subunits leads to the reduction in the intracellular content of RNA polymerase core relative to the bulk of proteins as much as approximately 1.5 fold. In addition, the activity of RNA polymerase is repressed in the stationary phase, as indicaated by the decrease of the nucleoidbound RNA polymerase, hence of functioning polymerase, of as much as 1.5 fold. Thus, the decrease of overall transcription activity in the stationary phase cells can be best explained by the reduction in both the concentration and activity of RNA polymerase. The observed coupling between the repression of RNA polymerase syntehsis and the increase of unused polymerase supports the autogenous regulation of rpo gene expression.