<i>Bacillus subtilis</i> σ^A and <i>Escherichia coli</i> σ⁷⁰ lacking σ region 1.1 are not released during transcription initiation and elongation.

Abstract

A "σ cycle" in which the initiation factor σ associates with RNA polymerase (RNAP) core enzyme to permit transcription initiation and dissociates from RNAP core enzyme to permit transcription elongation, has been proposed to occur and to be an essential step for σ-exchange, with all principal σ factors from all bacteria. These proposals were based on studies of the principal σ factor of <i>Escherichia coli</i>, σ⁷⁰, which generally, albeit not obligatorily, is released from RNAP upon the transition from transcription initiation to elongation. Here, we show that, in contrast to <i>E. coli</i> σ⁷⁰_, the <i>Bacillus subtilis</i> principal σ factor, σ^A, is not released and is retained on RNAP core throughout transcription elongation. We further show that a mutant <i>E. coli</i> σ⁷⁰ derivative lacking σ region 1.1 (σ R1.1) is not released and is retained on RNAP core throughout transcription elongation. We also observe that <i>B. subtilis</i> σ^A and the mutant <i>E. coli</i> σ⁷⁰ derivative lacking σ R1.1 interact much more stably with RNAP than full-length <i>E. coli</i> σ⁷⁰. Our results indicate that the σ cycle is not a universal phenomenon in bacteria.