Subunits of RNA polymerase in function and structure: IX. Regulation of RNA polymerase activity by stringent starvation protein (SSP)

Abstract

A 22,500 molecular weight polypeptide (22.5 K) stably associated with purified DNA-dependent RNA polymerase (EC 2.7.7.6) from Escherichia coli was found identical with the stringent starvation protein (SSP), which is the predominant protein synthesized in stringent strains under conditions of extreme amino acid starvation. The 22.5 K protein was dissociated from purified RNA polymerase by passage through a phosphocellulose column. The isolation of 22.5 K protein was also performed by DEAE-Sephadex column chromatography of polymerase previously dissociated with urea. Isolated 22.5 K protein considerably influences (mostly reduces) the activity of holoenzyme but not of core enzyme. The influence depends on the DNA template used and the salt concentration employed. In accordance is the finding that 22.5 K protein binds to holoenzyme but not to core enzyme lacking sigma subunit. The results suggest that the 22.5 K protein is involved in the regulation of transcription catalyzed by holopolymerase, in particular in stringent starved cells. Mechanisms whereby 22.5 K protein might participate as a regulatory molecule are discussed.