Effect of multiple copies ofrpoBCon the rate of RNA synthesis inEscherichia coli

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Abstract
Summary: The cloning of therpoBandrpoCgenes in a high copy number vector inE. coliincreased the amount of the encoded gene products, the β and β′ subunits of RNA polymerase. However, this unexpectedly caused a 30–50% decrease in RNA synthetic activity which alternatively induced a reduction of growth rate and enlargement of cell size, and decreased the DNA replication time. The results can be explained by autogenous regulation of the RNA polymerase genes by the ββ′ subunits. A relation between the decrease in number of transcription units and the observed higher rate of movement of DNA replication forks is discussed.