Purification and Comparative Properties of the Delta and Sigma Subunits of RNA Polymerase from Bacillus subtilis

Abstract

Bacillus subtilis delta protein is a 21500‐M_r polypeptide that can be isolated in association with RNA polymerase holoenzyme from uninfected bacteria and with modified forms of RNA polymerase from cells infected with phage SP01 [Pero, J., Nelson, J. and Fox, T. (1975) Proc. Natl Acad. Sci. U.S.A. 72, 1589]. Although no function has been assigned to δ protein in uninfected cells, this host polypeptide enhances the specificity of transcription by phage‐modified forms of RNA polymerase that contain SP01‐coded regulatory subunits. This report describes the purification of δ and σ proteins from uninfected B. subtilis and examines the comparative effects of these polypeptides on transcription by core RNA polymerase. Purified σ polypeptide was found to stimulate the transcription of phage DNA while having little effect on RNA synthesis with the synthetic DNA poly(dA‐dT) as template. In contrast, purified δ protein markedly depressed the transcription of poly(dA‐dT) while having little effect on enzyme activity with phage DNA as template. The inhibitory effect of δ protein on poly(dA‐dT) transcription was strongly dependent on the presence of KCl in the RNA synthesis reaction mixture.