The delta 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 (sigma) factors and an auxiliary subunit known as delta (delta). We have addressed the roles of the delta polypeptide in a model transcription cycle using the promoter and attenuator of the ilv-leu operon. We demonstrate that delta influences both the promoter selection and core recycling phases of the transcription cycle. The delta protein functions together with sigma as an initiation subunit of RNA polymerase. Remarkably, E sigma delta forms predominantly closed complexes at the P(ilv) promoter even at 40 degrees C, whereas E sigma forms open complexes. The presence of delta inhibits transcription at low temperatures, presumably because delta decreases the rate of open complex formation. In contrast, delta 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 delta on DNA-melting, we find that delta stimulates the amount of RNA synthesized from the P(ilv) leader region several-fold in multiple cycle reactions due to an increased rate of enzyme recycling. These results highlight the importance of delta in determining RNA yield during in vitro transcription.