Hyperproduction of the sigma subunit of RNA polymerase in a mutant of Escherichia coli.

A mutant of Escherichia coli K12 is described in which sigma and alpha subunits of the DNA-dependent RNA polymerase (EC 2.7.7.6) are produced at the rates much higher than in the normal strain. The rate of synthesis for sigma subunit was found to be at least 10-times higher, though the rapid degradation of sigma polypeptides accompanied with the accelerated synthesis precludes accurate estimation of the extent of hyperproduction. The alpha subunit synthesis was about 5-times higher in this mutant than in the control, and excess alpha polypeptides produced were as stable as the bulk of protein under the conditions employed. Genetic analyses of the mutant by conjugation and by transduction with phage P1 revealed that at least three distinct but closely linked mutations are responsible for hyperproduction of the sigma subunit; one (sig-1) is located very close to rif, and the others (sig-2 and sig-3) at the argH-bfe and metB regions, respectively. The results further indicate that the accelerated synthesis of alpha subunit is due to a mutation also located at the metB region. The present finding suggests that the synthesis of sigma subunit is subject to a complex control that can be affected by a number of cellular processes. The possible involvement of the core polymerase in determining the rate of synthesis of sigma subunit is discussed.