The δ subunit of bacillus subtilis RNA polymerase: An allosteric effector of the initiation and core-recycling phases of transcription

Abstract

RNA polymerase purified from Bacillus subtilis contains multiple sigma (σ) factors and an auxiliary subunit known as delta (δ). We have addressed the roles of the δ polypeptide in a model transcription cycle using the promoter And attenuator of the ilv-leu operon. We demonstrate that δ influences both the promoter selection and core recycling phases of the transcription cycle. The δ protein functions together with σ as an initiation subunit of RNA polymerase. Remarkably, Eσδ forms predominantly closed complexes at the Pilv promoter even at 40°C, whereas Eσ forms open complexes. The presence of δ inhibits transcription at low temperatures, presumably because δ decreases the rate of open complex formation. In contrast, δ has little or no effect on the overall rate of promoter localization and initiation. rate of elongation, or termination efficiency. Despite the inhibitory effect of δ on DNA-melting, we find that δ stimulates the amount of RNA synthesized from the Pilv leader region several-fold in multiple cycle reactions due to an increased rate of enzyme recycling. These results highlight the importance of δ in determining RNA yield during in vitro transcription. © 1994 Academic Press Limited.